relationships between water and feed intake during the growth … · 2009-09-09 · ratio between...

The dynamic relationship between water and feed intake in slaughter pigs

Master thesis (36 ECTS credits) by

Torben Leegaard Riis L9756

Department of Animal Science and Animal Health Royal Veterinary and Agricultural University

Copenhagen, Denmark March, 2003

The dynamic relationship between water and feed intake in slaughter pigs

Master thesis (36 ECTS credits) by

Torben Leegaard Riis L9756

Supervised by Anders R. Kristensen, Associate Professor Department of Department of Animal Science and Animal Health Royal Veterinary and Agricultural University

Department of Animal Science and Animal Health Royal Veterinary and Agricultural University

Grønnegaardsvej 3 DK-1870 Frederiksberg C

Denmark March, 2003

Abstract The recent development of a new system monitoring water consumption in growing pigs has stimu-lated the desire of investigating the relationship between water and feed intake in slaughter pigs over time. Hence, the objective of this study was to investigate time patterns and consistency in time patterns of the ratio between water and feed intake during the growth period in groups of slaughter pigs. Expected time patterns and levels of the ‘water/feed’ ratio in growing pigs were investigated by a literature review in combination with analysis of field data with young boars growing from ap-proximately 25 kg to 100 kg live weight. Data comprised approximately 670 pigs allocated on 6 batches within 1½ years time and was obtained at a central testing facility in the Danish breeding program. The results from literature showed that daily levels of the ‘water/feed’ ratio depended on age and possibly sex of the pigs. Climatic and physical conditions in the near environment also play impor-tant roles. Several other factors have more short-term impacts on feeding and drinking patterns (e.g. competitions levels and breed). Therefore 24 hours was chosen as an appropriate time interval for accumulation of feed and water intake data in order to obtain consistent time patterns of the com-bined ratio. Using random regression models analyses of daily ‘water/feed’ ratio, and water and feed intake curves were performed. The mean curve for the ‘water/feed’ ratio showed a gradually decreasing pattern over time (approx. 3.1 – 2.6).

Resumé Den nylige udvikling af et system til overvågning af vandforbrug hos grise har inspireret et ønske om at undersøge forholdet mellem vand- og foderoptagelse over tid hos slagtesvin. Derfor var for-målet med dette projekt at undersøge tidsmønstre og konsistensen i generelle tidsmønstre for for-holdet mellem vand- og foderoptagelse hos grupper af slagtesvin. Forventede tidsmønstre og niveauer af ”vand/foder” forholdet hos slagtesvin var undersøgt ved et litteraturstudium i kombination med analyser af feltdata med unge orner voksende fra ca. 25 kg til 100 kg levendevægt. Data indeholdt observationer for ca. 670 grise fordelt på 6 hold indenfor en 1½ års periode, og var opsamlet på en test station indenfor det danske avlsprogram. Resultaterne fra litteraturen viste, at daglige niveauer af ”vand/foder” forholdet afhænger af grise-nes alder og muligvis køn; men også klimatiske og fysiske forhold i grisenes nærmiljø spiller en væsentlig rolle. Adskillige andre faktorer har mere kortsigtet indflydelse på vand- og foderoptagel-sen (f.eks. konkurrenceniveauer og race). Derfor var 24 timer fundet som et passende tidsinterval for akkumulering af data for vand- og foderoptagelsen, mht. til at opnå konsistente tidsmønstre for ’vand/foder’ forholdet. Ved brug tilfældige regression modeller blev forløbet af daglige niveauer af ”vand/foder” forholdet og vand- og foderforbruget særskilt analyseret. Middelkurven for ”vand/foder” forholdet viste et gradvist aftagende mønster over tid (ca. 3.1 – 2.6).

Preface The present report has been prepared to meet the criteria of a Master thesis (36 ECTS credits) at the general M.Sc. Programme in Agricultural Science under supervision from Associate Professor An-ders R. Kristensen at the Danish Royal Veterinary and Agricultural University, Department of Animal Science and Animal Health. The National Committee for Pig Production, Danish Bacon and Meat Council has provided data material for analyses of this study and offered me the opportunity to work in their office facilities, which have been greatly appreciated. Several people have inspired and supported me during the project period. I would like to thank my co-supervisor Thomas Nejsum Madsen, The National Committee for Pig Production, Danish Bacon and Meat Council. Special thanks are also offered to Erik Jørgensen, Department of Agricultural Systems, Danish In-stitute of Agricultural Sciences, and to Henrik Wachmann, Verner Ruby and Maibritt Nielsen from The National Committee for Pig Production, Danish Bacon and Meat Council. Their inspiration and qualified guidance regarding statistical matters and practical handling of the relatively complex data material analysed has been greatly appreciated. I would also like to acknowledge and thank everybody in the Department for Production Systems at The National Committee for Pig Production for including me in the daily working and social envi-ronment in the department. _______________________________

Torben Leegard Riis, L9756 Copenhagen, March 14th, 2003

Contents

1 Introduction .....................................................................................................................................1

1.1 Formulation of the problem........................................................................................................2 1.2 Objective ....................................................................................................................................2 1.3 Procedure....................................................................................................................................3 1.4 Delimitation................................................................................................................................3

2 Factors influencing patterns and levels of water and feed intake in growing pigs ...................4

2.1 General characteristics of drinking and feeding patterns in pigs ...............................................4 2.2 Pattern changes of ‘water/feed’ ratio over time .........................................................................6

2.2.1 Diurnal variations................................................................................................................9 2.3 Social aspects ...........................................................................................................................11

2.3.1 Group size .........................................................................................................................12 2.3.2 Competition.......................................................................................................................14

2.4 Climate and light conditions ....................................................................................................17 2.5 Other factors.............................................................................................................................24

2.5.1 Housing conditions............................................................................................................24 2.5.2 Feed composition ..............................................................................................................25 2.5.3 Health conditions (diseases)..............................................................................................25 2.5.4 Human activity ..................................................................................................................26

2.6 Breed and sex ...........................................................................................................................26 2.7 Chapter summary .....................................................................................................................28

3 Experimental study (field data with slaughter pigs) ..................................................................31

3.1 Materials...................................................................................................................................31 3.1.1 Pigs ....................................................................................................................................32 3.1.2 Housing conditions............................................................................................................32 3.1.3 Feed, bedding material ......................................................................................................34 3.1.4 Working procedures, registrations, data logging, medical treatments, etc. ......................34 3.1.5 Preparation of data ............................................................................................................34 3.1.6 Limitations ........................................................................................................................35

3.2 Preliminary data analysis .........................................................................................................35 3.2.1 Data validation ..................................................................................................................35 3.2.2 Time interval appropriate for studying ‘water/feed’ ratio.................................................39 3.2.3 Statistical methods.............................................................................................................41

3.3 Results ......................................................................................................................................45 3.3.1 Raw or transformed response values.................................................................................45 3.3.2 Statistical test and model reduction...................................................................................46 3.3.3 Final models ......................................................................................................................48 3.3.4 Model check ......................................................................................................................51 3.3.5 Model performance ...........................................................................................................55

3.4 Chapter summary .....................................................................................................................59

4 Discussion.......................................................................................................................................60

4.1 Conclusions ........................................................................................................................67

5 Future perspectives ..................................................................................................................70

References .........................................................................................................................................71

Appendix ...........................................................................................................................................74

Chapter 1 Introduction 1 ________________________________________________________________________________

1 Introduction As agricultural production exists in a world of increasing cost levels and changing consumer de-mands, it has become necessary to focus on possible ways of optimising production processes and minimising or avoiding possible losses. The challenge is to obtain a higher information level about production processes whilst being able to reduce labour intensity and thereby diminish economic costs. The improved information level must be utilised by an optimal allocation of the production relevant factors. In other words, having such information available should enable the stockman to take the precautionary actions needed, or make appropriate adjustments. Systems for improved management in animal production based on sensor technology are being developed and various sys-tems are already commercially available (Frost et al., 1997). The application of integrated monitor-ing system techniques, in which information from sensors, databases, mathematical models and knowledge bases are combined and interpreted, can enable the maximum potential of this informa-tion to be realised (Frost et al., 1997). Research has indicated that monitoring the diurnal drinking pattern of pigs can provide information relating pattern changes to animal health. Using methods described by West and Harrison (1997) data is transformed and interpreted by using a combination of dynamic linear modelling (DLM), Kalman filtering and a Cusum control chart. Madsen (2001) claims that outbreaks of diseases like diarrhoea can be predicted by such a system up to 24 hours prior to clinical detection. The monitor-ing system based on water consumption has been implemented as a commercial software package (FarmWatch), which is available for pig production (Madsen, 2001). For the potential of improved herd management it is desirable to improve the amount and the quality of information obtainable from monitoring systems such as Farm Watch. In traditional pig herds’ recordings of feed consumption are often made on larger groups of animals or the entire herd. Under practical conditions with a water monitoring system like FarmWatch, knowledge about consistency in patterns of the ‘water/feed’ ratio could be utilised to provide in-formation on the distribution of feed consumed between groups of pigs. This would produce infor-mation about productivity (feed conversion efficiency) in different groups of pigs if growth per-formance was already monitored. To obtain information about feed consumption by means of moni-toring water intake a consistent pattern of the ‘water/feed’ ratio would be necessary over a shorter or longer time horizon. When discussing consistency of the ‘water/feed’ ratio, some recurrent pat-tern according to time must be present, however it could be affected by random variation. In other words, a consistent pattern would imply some kind of predictability about the ‘water/feed’ ratio ac-cording to the time of observation and specific factors known to have an impact. Topics affecting the consistency in patterns of ‘water/feed’ ratio in growing pigs are central aspects of this study.


The present study was encouraged by a desire to investigate the relationship between water and feed intake during the growth period of slaughter pigs, as it was believed that such information could be utilised in the development of new tools for improved management in animal production. Bigelow and Houpt (1988) gave further inspiration as their study indicated that a relatively stable ratio be-tween the level of water intake and feed consumption in growing pigs exists. Other studies have shown a strong correlation between feed intake and the daily weight gain in slaughter pigs (e.g. Labroe et al., 1994, Young and Lawrence, 1994), although other studies have shown variation in the feed conversion ratio of growing pigs. It is believed that the analysis of this study could contribute to the general understanding of possible relations between patterns of water intake, feed consumption, and the actual growth curve of the animals. Future perspectives are that such knowledge then could be used in the development of new methods to obtain a dynamic control regarding animal performance and feed consumption between groups of pigs in modern production systems.

1.1 Formulation of the problem In order to examine the pattern and consistency in pattern of ‘water/feed’ ratio in growing pigs it is relevant to analyse the patterns of both water and feed intake over time. To examine these patterns it is necessary to study the possible factors that affect water and feed intake separately. Determining these factors is desirable, because it would give information about possible impacts on the com-bined ratio. It would also give information on how general patterns adapt to different conditions (e.g. housing and climatic conditions). Finally, it is imperative to determine odd incidences that could cause violations of water and feed intake patterns. A central point is to find an appropriate interval for accumulation of feed and water intake data in order to analyse the time patterns of the ‘water/feed’ ratio.

1.2 Objective The objective of this study is to investigate expected time patterns and consistency in patterns of the ratio between water and feed intake during the growth period in groups of slaughter pigs. The hy-pothesis is that the ratio between water and feed intake follow a consistent pattern though it could be associated with some change, as the pigs grow.


1.3 Procedure This project is based on knowledge obtained through a literature review in combination with the analysis of data obtained from an experimental farm run by The National Committee for Pig Pro-duction in Denmark. The process of the first study was to explore the possible influences on the development in patterns of water and feed consumption in growing pigs. During a visit to the experimental farm in April 2002, specific conditions regarding pigs, housing conditions, work procedures, etc. were studied and evaluated in relation to the areas of interest for this study. Combined knowledge obtained from the farm visit and general aspects of relevance identified in the course of literature research was used to schedule the work procedure for carrying out this project. The first part of the report reviews expected traits of drinking and feeding behaviour in growing pigs as described in literature, and also how different factors would affect water and feed intake pat-terns. Knowledge obtained from the literature reviewed has been used in the analyses of data. In chapter 4 the results of the analyses are discussed.

1.4 Delimitation The analyses of this study (statistical and literature review) mainly consider growing pigs kept un-der indoor conditions and fed on dry meals. How different medical conditions would affect patterns of water and feed intake is not described in detail. Limitations as such therefore play an essential role in the discussion and overall evaluation of this study.

Chapter 2 Factors influencing patterns and levels of water and feed intake in growing pigs 4 ________________________________________________________________________________

2 Factors influencing patterns and levels of water and feed intake in growing pigs The ratio between water and feed intake in growing pigs is of particular interest for this study. It is hypothesised that knowledge about patterns and stability in patterns of ‘water/feed’ ratio could im-prove information utilisable from water monitoring systems as described in the introductory chap-ter. To explore the general patterns of ‘water/feed’ ratio and possible impacts on the consistency in patterns it is necessary to determine factors behind eating and drinking behaviour separately. The role of this chapter is to describe influences on eating and drinking behaviour in growing pigs. The influences in focus are those that should be considered if analysing patterns of ‘water/feed’ ratio in growing pigs under practical conditions within shorter or longer time intervals, as it is also desirable to find an appropriate time interval for accumulation of data. Systematically are influences of physiological and social matter as well as physical conditions in the surroundings described. Results of this chapter in conjunction with results of own data analysis are discussed in chapter 4.

2.1 General characteristics of drinking and feeding patterns in pigs Feed (and water) intake in monogastric animals is regulated by several mechanisms such as hormo-nal and nervous regulation (McDonald et al., 1995). More specifically the regulation is controlled by chemostatic and thermostatic mechanisms, though sensory appraisals and physiological factors of different kinds also play a role. It is self evident that water requirements will be related to the amount of feed eaten, feed composition, ambient temperature, the need to evaporate water from the lungs, and the amount of toxic products to be cleared from the system via the urine. The animal ob-tains its water from three sources: drinking water, water present in the feed and metabolic water, this last being formed during metabolism by the oxidation of hydrogen-containing organic nutrients. Water is lost from the body by four main channels: the lungs, the skin, the intestines and the kid-neys. Requirements are determined by the magnitude of these depletions, together with the amounts, which are included in new tissue formed during growth (or pregnancy and milk produc-tion) (McDonald, 1995). Under practical conditions structure of drinking patterns and feeding behaviour are influenced by the state of the individual animals and by a variety of factors in the surrounding environment (e.g. Bigelow and Houpt, 1988; Haer and Vries, 1993; Petherick et al., 1989; Turner et al., 2000; Young and Lawrence, 1994). The state of the individual pig is related to sex, breed, age, and nutritional and physiological status. Factors in the environment affecting the drinking and feeding behaviour can be sub grouped into categories such as influence of human activity and factors associated with housing and climatic conditions.


Anand (1961) stated that the voluntary water intake by mammal is usually correlated with feed in-take, and the pig appears to provide no exception to this general rule. Pigs being prandial drinkers (water intake associated with feeding) has been recognised in several studies (Houpt, 1985; Ingram et al., 1980, 1985; Musial et al., 1999; Bigelow and Houpt, 1988). Water is also the most important of appetite stimulators, as Whittemore (2000) reports that a simple expedient of adding water to feed can increase the voluntary intake of pigs by at least 5-10%, and occasionally up to 30%. The ratio between the daily water and feed intake is influenced by several factors such as feed composi-tion, temperature, access to feed and water, and social factors. Young pigs need more water per kg of live weight (LW) than older ones, due to their greater surface area of body and lung in compari-son to weight, and due to the tendency for the urine of younger animals to be more dilute (Whitte-more, 2000). It was also reported by Whittemore (2000) that growing pigs are conventionally (and erroneously) understood to desire a water to dry ratio of 2:1, as recent research have suggested the following formula to describe water requirements in growing pigs. This formula is a function of feed intake (I):

Minimum water need (litres) = 0.03 + 3.6 x I (kg) (Whittemore, 2000) In addition to the results of the formula Whittemore (2000) claims that these water requirements are marginal and, given free access, a water to dry feed ratio of 5:1 in growing pigs is common. Rela-tive constancy in the ‘water/feed’ ratio suggests a good control of water intake that balances the load of osmotically active substances ingested in the feed, but there are obviously different under-standings of the general ratio between levels of water and feed consumption in growing pigs. As we shall see in section 2.4.2 water requirements are also dependent on water content in the diet and feed composition in general. Chwalibog (1997) stated that a general guideline for the water re-quirement in growing pigs is 2.1 l/kg dry matter (DM). Gill and barber (1993) investigated voluntary water intake according to different feed allowances varying from 80g to 100g of dry feed/kg0.75 (metabolic live weight) to a group of 32 young growing pigs. The results showed a tendency of a reduced ‘water/feed’ ratio with increasing feed allowances (table 2.1), however the results were not statistical significant. In contrast performance data of the pigs differed between treatments. Table 2.1 Performance and water use by dry fed growing pigs (mod a. Gill and Barber, 1993).

Feeding level (g/kg0.75) 80 90 100 110 P-value

Water use (l/day) 3.29 3.45 3.53 3.60 NS Growth rate (kg/day) 0.39 0.55 0.57 0.71 <0.05 Feed conversion ratio 3.34 2.58 2.80 2.42 <0.05 ‘Water/feed’ ratio 2.65 2.43 2.21 2.08 NS


The tendency in pattern observed by Gill and Barber (1993) was also consistent with results re-ported by Yang et al. (1981) who found that pigs will minimize the ‘water/feed’ ratio when fed ad libitum and take additional water, presumably to produce feelings of satiety, when fed restrictively.

2.2 Pattern changes of ‘water/feed’ ratio over time Pattern changes of the ‘water/feed’ ratio in relation to pigs’ age are poorly investigated. However, few authors report results of feed (and water) intake in relation to the LW of growing pigs and, one of them is Bigelow and Houpt (1988). In the LW range from 10 to 40 kg an average of 94% of the total water intake was prandial, with proportionally less drunk independent of meals. Prandial drinking fell to 75% in the 40 to 70 kg LW range and then remained at this or a lower percentage of the total daily intake in larger pigs. Pigs being prandial drinkers could suggest a high stability in figures of the ‘water/feed’ ratio within a relatively short time period, however the results of Bigelow and Houpt (1988) indicated variation in the pattern observed. Figure 2.1 shows the daily ‘wa-ter/feed’ ratios observed by Bigelow and Houpt (1988) for different LW ranges (10-130 kg). Ac-cording to their results, there appeared to be a relative constancy of water to feed ratio (averaged over many days).

0,0

1,0

2,0

3,0

10-20

20-30

30-40

40-50

50-60

60-70

70-80

80-90

90-100

100-110

110-120

120-130

Live Weight range (kg)

Mea

n 'W

ater

/feed

' rat

io (m

l/g)

Figure 2.1 Daily ‘Water/feed’ ratios of growing pigs. Mean values for each LW class (mod. a. Bigelow and Houpt, 1988). The two peaks shown in figure 2.1 were unexplained, however Bigelow and Houpt (1988) reported a significant variation in the ratio on a day-to-day basis. As seen in fig 2.2 with registrations from a single pig, this balance was not precise on a day-to-day basis. Bigelow and Houpt (1988) claimed that daily variations in ‘water/feed’ ratio generally were due to variations in water intake, rather than of feed, as also reported by Mount et al. (1971).


Figure 2.2 Daily ‘water/feed’ ratios for a single pig showing day-to-day variation over 30 days (Bigelow and Houpt, 1988).

The relatively constancy in average ‘water/feed’ ratio found in groups of pigs by Bigelow and Houpt (1988) was in contrast to earlier results reported by Pieterse (1963), who found a declining ratio according to increasing live weight (age) of growing pigs (table 2.2) in a study where pigs were fed restrictively according to LW. Table 2.2 Mean ‘water/feed’ ratio at different live weights (Pieterse, 1963). Live weight (kg) 23 34 57 68 Water/feed ratio (l/kg) 3.5:1 3.3:1 2.6:1 1.7:1

In the experiment of Pieterse (1957), 6 Large White and 6 Landrace pigs were fed on a maize, wheat and fish meal (7.5%) from 18 to 45 kg; for the succeeding period the fish meal was elimi-nated. In both periods, the amount of water was mixed with the meal when it was fed, and after the ration had been consumed the pigs were allowed free access to water. In the study of Bigelow and Houpt (1988) 6 female pigs grew from 10 to 130 kg (3 to 6 months of age) as daily feed intake increased threefold, while meal frequency declined from an average of 14 to 7 per day. As no significant difference in meal duration was found, the increases in meal size and daily intake were apparently due almost to a distinct increase in the rate of eating (g/minute). Such pattern changes have also been found in other studies where the total eating time tended to decrease at the same time meal size increased due to increased rate of eating as the pigs grew larger (Hyun et al., 1997; Labroue et al., 1994; McDonald et al., 1991; Morgan et al., 2000; Nielsen et al., 1995). Labroue et al. (1994) studied 428 pigs of both Large White and French Landrace breed in four batches from January to June 1992. The pigs were observed during a test period from 35 to 95 kg liveweight for boars and from 35 to 100 kg for castrated males. Data were collected in 42 pens with 9 to 14 pigs, boars and castrated being never present together in the same pen. Table 2.3 shows the general evolution of behavioural criteria for eating in growing pigs found by Labroe et al. (1994).


Table 2.3 Evolution of behavioural criteria over week 2, 6, and 10 (mod. a. Labroe et al, 1994). Trait means +/-sd Week number (approx. live weight kg) 2 (40) 6 (60) 10 (90) Meal size (g) 278 +/-118 425 +/-185 621 +/- 261 Time per meal (min.) 10.2 +/-3.8 11.1 +/-4.5 11.4 +/-4.6 Number meals/day 7.2 +/-2.6 6.6 +/-2.9 5.3 +/-2.2 Feed intake/day (g) 1.757 +/-351 2.363 +/-394 2.810 +/-426 Eating time/day (min.) 63.7 +/-16.3 60.0 +/-15.0 49.6 +/-11.7 Rate feed intake (g/min.) 28.6 +/-6.4 40.9 +/-8.9 58.8 +/-12.6

Number of meals per day showed a continuous decrease throughout the growth period, from 7.2 meals per day in week 2 to 5.3 in week 10, while average meal size increased from 278 g to 621 g on average. A linear increase in feed intake according to live weight of growing pigs has been found in several studies. Hyun et al. (1997) found such results in a study with 120 crossbred pigs from 27 to 81,5 kg LW, and so did Morgan et al. (2000) studying a group of 16 pigs growing from approx. 17 to 52 kg LW over a 35 day period. Slader and Gregory (1998) similarly found a linear relationship in a trial with 200 Large White pigs from weaning to slaughter. Liang and Wood-Gush (1984) studied the feeding behaviour of 4 castrated boars over 24 hours at four LW stages: 20, 40, 60 and 80 kg when fed ad libitum. The pigs were exposed to two different light regimes in pairs of two as further described in section 2.4, but a general result was that LW affected the number of meals, with youngest taking most. When the pigs weighed between 20 and 70 kg, there similarly was a simple linear relationship between feed intake and LW. The slope of the graph comparing LW and feed intake tended to be steeper for pigs weighing 15-20 kg as shown in figure 2.3. However for pigs weighing more than 70 kg, the relationship was not so straightfor-ward.

Figure 2.3 The relationship between LW and feed intake in the 4 pigs on the two lighting regimes (Liang and Wood-Gush, 1984).

An interesting result was the change in feeding behaviour in pigs from around 20 kg to 80 kg LW. The trend in feed intake within this bodyweight range could be divided into 3 stages. In the first stage, in which the pigs weighed between 15 and 20 kg, the feed intake of the pigs increased more sharply than in other stages. In the second stage, in which the pigs weighed between 20 and 70 kg, the increase in the rate of feed intake lay between the first and third stages. In the third stage, in


which the pigs weighed between 70 and 80 kg, there was a large variation in feed intake and the rate of increase was the lowest of the 3 stages. There was a large variation in eating speed between indi-viduals, and it increased with increasing LW. The total feeding time tended to decrease with an in-crease in LW, although the differences also did not reach a significant level. Figure 2.4 shows the daily feeding pattern with different LW’s (20, 40, 60 and 80 kg).

20 kg LW 40 kg LW 60 kg LW 80 kg LW

Figure 2.4 The distribution of feeding by a pig over the day when 8.5 h of light and 15.5 h of darkness. The chart shows the number of seconds devoted to feeding every 5-min. period. The graphs show the pattern of feeding at different LW stages. Each graph covers the period from 0930 H on one day until 0900 H on the next (Liang and Wood-Gush, 1984).

It appears that pigs as they get older change their feeding behaviour to fewer larger meals with an increased consumption rate. Figures of the ‘water/feed’ ratio appear to be rather constant averaged over many days, however this balance is not precise on day-to-day basis for individual pigs. Whether the ‘water/feed’ ratio is constant or characterised with a change in level according to age of the pigs is not quite clear, although the older study by Pieterse (1963) indicated a declining ‘wa-ter/feed’ ratio when pigs where fed restrictively. Results from literature also revealed a relatively linear relation of feed intake according to LW (within LW range 20-70 kg). For pigs lighter than 20 kg the curve is rather steep, whereas for pigs heavier than 70 kg the patterns is not so distinct. 2.2.1 Diurnal variations From focussing on age related characteristics we will now look closer at diurnal patterns. A strict diurnal pattern in the feeding behaviour has been recognised by several authors who have investi-gated the behaviour on different groups of pigs (e.g. Haer and Vries, 1993; Hyun and Ellis, 2001; McDonald et al., 1991; Young and Lawrence, 1994). However, these patterns appeared to vary in structure, as some studies found a single peak of the daily feed intake in the morning (Hyun et al., 1997; Young and Lawrence, 1994) whilst others found two (Bigelow and Houpt, 1988; Slader and Gregory, 1988; Feddes et al., 1989; Nieanaber, 1990; Haer and Vries, 1993; Brown van der Steen, 1990). Young and Lawrence (1994) stated that a strong diurnal pattern in the feed intake, with two peaks (bimodal), one at the beginning and one at the end of the light period can be found in pigs older than 6 weeks of age.


Other studies have similarly shown that there exists a strict diurnal pattern in the water intake of growing pigs (Gill and Barber, 1993; Turner et al., 1998; Madsen, 2001). Figure 2.5 shows such pattern observed by Gill and Barber, (1993), from a trial where growing pigs were offered liquid feed meals with water contents varying from ratios of 2:1 to 3.5:1.

Figure 2.5 Diurnal patterns of water intake according to treatment by liquid-fed pigs (Gill and Barber, 1993).

Pigs are considered to be most active during daylight, with most of their feed intake occurring dur-ing this time (Ingram et al., 1980, 1985). Bigelow and Houpt (1988) found that 64% of daily feed intake and 68% of water intake was during a 12-h light period. These results were obtained when artificial light was provided for 12 hours in a windowless environment and with a 3,5 W red dim light during the dark hours. Ingram et al. (1985) reported that unlike many other mammals the young pig can synchronize its activity to a non-diurnal rhythm without affecting growth and gener-ally with exposure to constant light the cyclic variations are lost within only a few days. These pat-terns contrast with those for other species in which it is found that in the absence of temporal cues, rhythms continue with a periodicity of about 24 hours (Ingram et al., 1985). In general, mammals have a narrower range of entrainment than birds, and insects have a wider range than vertebrates (Aschof and Pohl, 1978). Some of the hormones which are of major importance, are known to be secreted in phase with sleep, meals and light (Ingram et al., 1985). It was reported from a study of Nienaber et al. (1990) with 21 crossbred gilts from 28 days of age that 75.2% of eating activity and feed consumption occurred in daytime hours (0700 - 1900 H) when 74.8% of the feed was consumed. The percentage consumed during the lighted period re-mained relatively constant over the entire period of the study with an overall range of 77.4% at 11 weeks to 72.6% at 14 weeks. This value was somewhat higher than the average 64% eaten during daytime reported by Bigelow and Houpt (1988). Their results showed that the portion consumed


during daylight (0700 to 1900 H) varied from 50 to 75% of total daily feed intake. Nienaber et al. (1990) reported that eating activity during the day was bimodal (2 peaks) or there was a period of lower activity sometime around or before noon. Eating activity was greatest from 0700 to 0900 H and from 1300 to 1600 H. Pigs appear to have a relatively distinct pattern of water and feed consumption from about 6 weeks of age, however patterns appear to vary in structure. The drinking and feeding behaviour is gener-ally following day light patterns with one or two daily peaks of activity. It appears that the diurnal patterns are rather distinct, however conditions in the local environment may cause variation, that should be considered when analysing the patterns of ‘water/feed’ ratio in growing pigs. Young and Lawrence (1994) suggested that differences in feeding behaviour is influenced by social factors, as group-housed pigs were expected only to show a single peak pattern whereas individually housed pigs were expected to show a two-peak pattern. Pigs can generally synchronise their diurnal activity due to changes in light conditions, matters of competition, etc. without adverse effects on animal performance, as we shall see in later sections.

2.3 Social aspects That social factors can have an impact on drinking and feeding patterns of growing pigs has been reported in literature. Young and Lawrence (1994) claimed that social factors could influence the feeding behaviour of pigs as group-housed pigs often show synchronised feeding behaviour as a result of social facilitation. Young and Lawrence (1994) also suggested that social facilitation can lead to competition for access to the feeder where animals are housed with less feeding places than animals. Several studies have shown that pigs housed in groups eat faster, have a higher feed intake per meal, less eating time per day and a lower daily feed intake than pigs penned individually (e.g. Patterson, 1985; Haer and Merks, 1992; Hyun and Ellis, 2001). Social facilitation affecting the feed intake is also called allelomimetic feeding behaviour, one pig feeding within a group stimulate oth-ers to do so too. If it can induce pigs to eat more, then it will benefit the growth of pigs. However, this behaviour may induce all pigs in a group to go to the through at the same time and thus cause competition, which may result in some inferior animals having less chance to eat. Therefore, whether allelomimetic behaviour causes an increase or decrease in feed intake is not quite certain and it might be dependent on the availability to a feeder. From the study (described in section 2.2) of Liang and Wood-Gush (1984) it was concluded that allelometic feeding behaviour did not de-crease with increasing LW of the pigs, as they grew from approx. 15-80 kg. Young and Lawrence (1994) further reported that diurnal variation in feeding behaviour is not ex-plainable solely in terms of social synchrony and facilitation. This was concluded on results of a study on the feeding behaviour of 5 groups of 10 pigs, balanced for sex end initial LW (mean start-ing and finishing weight: 32.1 kg vs. 68.5 kg). Feed consumption was monitored on an electronic


feeding system (single space) for 38 days. Social competition appeared to affect physical perform-ance in the system most strongly through its influence on feeder occupation time and total feed in-take. It was concluded that although social synchrony and facilitation was not the only factor having an impact on the feeding behaviour, it did play an important role. Turner et al (2000) claimed that competition for access to a limited resource such as a feeding sta-tion or a drinking bowl might be allocated disproportionately to different members of a group with pigs. This statement is also consistent with results of McBride et al. (1964) and Hansen et al. (1982), as they found a positive correlation between social rank and performance of growing pigs especially with restricted access to feed. This was apparently due to the effect of higher competi-tion. It therefore appears that any factor having an impact on the competition between individuals also may play a significant role in the drinking and feeding behaviour of growing pigs. Pigs synchronise their patterns of activity in groups, which also influence diurnal water and feed intake patterns. Social facilitation can lead to increased competition for feeders or drinkers at peak hours of activity. Restrictions in access to feeder or drinkers can increase rate of intake, but further aspects of a restricted access are discussed in section 2.3.2. Now we will concentrate on social in-fluences related to differences between group sizes.

2.3.1 Group size Ingram et al. (1980) who observed groups of weaner pigs and single pigs for a period of four weeks found that single pigs had less well defined rhythms than those kept in groups. They suggested that this was related to a tendency of animals modifying their behaviour to conform to the predominant pattern of the group. This means that individual animals predominantly showing a nocturnal behav-iour would adjust to the diurnal pattern shown by most other group members due to social facilita-tion. It was also found that in pigs kept individually the extent to which rhythms of activity and feed and water intake persisted was very variable. Some pigs appeared to continue the rhythm after in-clusion into a group, and it was suggested that the inclusion of such an animal might strengthen the rhythms displayed by other group members. More specifically Hyun and Ellis (2001) found that pigs in groups of 12 consumed 8,8 % less feed per day and grew 6,4 % slower than others in groups of 2. However feed conversion efficiency was not different between the different group sizes. The results of Hyun and Ellis (2001) were obtained from a trial with finishing pigs in groups of 2, 4, 8, and 12. A total of 416 hybrid pigs (PIC line 26 x Camborough 15) participated over a period of 4 weeks (approx. 22 – 48 kg LW). The pigs were kept in pens with part-slatted, part-solid floor, and a constant floor space allowance of 0.8 m2 per pig. The overall results from the study suggested that growth rate and feed intake of growing pigs given a space allowance greater than that required for maximum growth performance is decreased as group size increases from 2 to 12 pigs. Hyun and Ellis (2001) reported that these results con-


trasted with earlier result from a Ph.D. thesis by Y. Hyun with finishing pigs in groups of 2, 4, 8, and 12. Those results showed no effect of group size, on average daily feed intake, average daily weight gain, or feed conversion efficiency. Nielsen et al. (1995, 1996B) reported that whilst individually kept animals have many small meals, group housed pigs achieve the same daily feed intake, but adapt to the social environment by chang-ing their feeding pattern to have fewer, larger meals (fig. 2.6).

Figure 2.6 Mean feed intake per visit plotted against the mean number of visits per day for each individual animal (n=148). The isoline represents combinations of x and y resulting in daily feed intake of 1.490 g/day (the overall mean) (Nielsen et al., 1995).

The results were obtained in a trial with 150 crossbred (Large White x Landrace) entire male pigs (approx. 30 – approx. 60 kg LW) over a period of 29 days. Three replicates were carried out, each using 50 animals allocated to one of four different group sizes: 5, 10, 15, or 20 pigs per group. Pen size was kept in proportion to the number of pigs (1.06 m2 /pig), and the drinker allocation was 1, 2, 2, and 3 water bowl(s) for group size 5, 10, 15, and 20 respectively. Each pen had one single-space computerised feeding station. Nielsen et al. (1995) concluded that group-housed growing pigs mod-ify their feeding behaviour when group size reached 20 as a response to the increased competition. Although the increasing group size had an influence on feeding behaviour the results showed a similar daily intake, growth rate, and feed conversion efficiency for all group sizes. That social factors according to group sizes play a role regarding patterns of water and feed con-sumption is clear. Single pigs generally have many feeder visits consuming smaller meals whereas pigs in groups tend to modify their behaviour and have fewer but larger meals. Increased competi-tion because of larger group size does normally not affect daily total intake, however contrasting results were reported by different authors. More attention to this aspect will be paid in the next sec-tion.


2.3.2 Competition Social facilitation play a role regarding diurnal patterns of growing pigs feeding behaviour, and therefore more focus needs to be put on possible restrictions in the access to resources such as feed-ers or drinkers. Feeder access As described in the previous section, Nielsen et al. (1995) observed that the daily feeding time aver-aged around one hour per pig, which in theory gave a maximum of 24 pigs per group using a single space feeder to allow sufficient feeding time for all individuals. The results also showed that pigs kept in groups of 20 ate significantly faster than pigs in smaller groups and consequently had a shorter daily feeder occupation. Walker et al. (1991) performed a study with 360 pigs penned in groups of 10, 20, and 30 with one mono-place feeder which was the only source of both feed an water. The housing conditions had fully slatted floor pens providing 0.6 m2 per pig on all treatments. The water consumption was measured in 2 of 6 replicates. Results of the study showed that groups of 30 animals occupied a mono-space feeder 92% of the time, and the two peak eating pattern usually displayed by group housed pigs disappeared as the animals were feeding through the night. The results also showed that the number of pigs per feeder could be increased considerably without reducing growth rate. The diurnal pattern of feeding described elsewhere, with 2 peaks of activity before and after midday, was observed most clearly with 10 pigs per feeder. Feeding activity during the night, and more es-pecially in the middle of the day, increased with more pigs per feeder and in the earlier weeks of the experiment. It was concluded from the almost continuous occupation of the feeder that the pig to feeder ratio (30:1) had reached its maximum for single space feeders without adverse effect on life performance of the pigs. There were no differences in meal overall growth rates or in the variation within pens, however feed conversion was better for the 10-pig treatment than for the two other treatments. Apparent feed intake was lower and growth rate tended to be reduced in the first two weeks of the experiment with 30 pigs per feeder, while the effect of treatment on feed conversion was greatest in the mid-growth period. With reducing group size, feeder occupation declined, but the time spent per visit increased. Feeder occupation also declined with time owing to a reduction in the number of visits per pig, which was partially offset by increased time per visit. The number of pigs queuing to use the feeder increased with group size but decreased with time, except in the smallest group, giving a significant interaction. For individual pigs, time spent at the feeder and the number of visits ranged from 5 min. to 140 min. and from 5 per 24 hour to 65 per 24 hour, respec-tively. There were no significant treatment effects on either mean growth rate or on the variation in daily gain within pens as shown in table 2.4.


Table 2.4 The effect on overall growth performance of the number of pigs per mono-place feeder. The pigs grew from approx. 37 to 90 kg LW (mod. a. Walker et al., 1991). Pigs per feeder 10 20 30 P-value Apparent feed intake (kg/day) 2.18a 2.34b 2.31b <0.05

Mean 811 797 807 N.S. Live weight gain (g/day) s.d. within pens 96.3 96.1 91.0 N.S.

Feed/gain (g/g) 2.70a 2.93b 2.87b <0.05

Apparent feed intake decreased and feed conversion was improved with the lowest number of pigs per feeder. The absence of a treatment effect on the variation in growth rate within pens supports findings of Petherick et al. (1989) and Albar and Granier (1989). This implies that pigs being sub-ject to competition for resources such as feeders or drinkers to a certain degree can compensate by changing their behaviour. Another interesting finding was that the growth rate of individual pigs was not related to time spent in the feeder, even within treatments. It may be that the eating pattern for individuals varies from day to day. It is also possible that pigs spending less time in the feeder were eating and drinking faster. The mean overall consumption of water was 1.78 l/kg diet with dif-ferences between the two replicates (1.65 and 1.90 l/ kg) and between 10, 20 and 30 pigs per feeder (1.65, 1.80 and 1.89 l/kg). Variation in the ratio between groups and within groups was not de-clared. This shows that the water intake in relation to feed intake increased in the larger groups for unknown reasons according to Walker et al. (1991); however, the specific results could be related to feeder and/or drinker access. Water access Only a few studies have investigated the drinking pattern of growing pigs and the influence of drinker allocation to different group sizes of pigs. McDonald et al. (1996) studied the effect of drinking through space on the performance and behaviour of growing pigs in large groups deep-bedded straw. To determine drinking space requirements, four mixed sex groups of 42 pigs (starting weight approx. 34 kg) were allocated to four different treatments. The starting weight of the pigs was subject to some variation within groups. The groups had a drinking space allowance of 0.62(A), 1.60(B), 2.75(C), and 4.85(D) cm per pig in a continuous length of drinking trough respec-tively. The smallest through only provided enough space for one pig to drink at the time and ad libi-tum feed hoppers were placed two meters away from the drinking trough. No significant treatment differences were found in daily gain, feed intake, feed conversion efficiency, or water to feed ratio, though specific levels of feed intake or ‘water/feed’ ratio were not published. Mean water consump-tion was 5.44, 4.98, 5.69, and 5.52 (s.e. 0.068) l/day per pig for A, B, C, D, respectively. The differ-ences were a result of varying number of visits rather than length of time per visit. A possible ex-planation of the lack in results may be that the practical design of treatments did not represent suffi-cient restriction in the drinking water access to affect either the ‘water/feed’ ratio or other traits. Turner et al. (1998, 2000) studied influence of drinker allocation to different group sizes of pigs. This was done on a 2 x 2 factorial design of two nipple drinker to pig ratios (1:10 vs. 1:20) yielding


four treatment combinations as group sizes of 20 and 60 were investigated. 640 large White x Land-race growing pigs (start weight 36 +/- 5.0 kg) were allocated to 1 of the 4 treatments for 5 weeks. To investigate possible effect of seasonal variation four replicates over time were allocated over a period from January to July. In the trial artificial light was provided for 8 hours daily and each group comprised of 55% males and 45% females, and floor space allowance per pig were kept con-stant. Figure 2.7 shows the diurnal distribution of drinking time observed for three weight catego-ries of pigs in the same pen (heavy 41.9 s.e. 0.51 kg; medium 35.7 s.e. 0.51 kg; and light 30.9 s.e. 0.63 kg), when treatments were pooled. Data for the 24-hour period was recorded by video analysis as registrations from each pen was segmented into six blocks of 4 hours.

Figure 2.7 Percentage of total daily drinking time occurring during 4 hour blocks for each weight category when treat-ment was pooled (Turner et al., 2000).

A strong diurnal pattern was recognised from the results shown in the diagram. The mean drinking bout duration was not significantly affected by time of the day or by weight category (28.1, 24.4 and 25.9 s.e. 2.70 for heavy, medium and lightweight pigs in the same pens. Although, the results did not show significant variation in the total water intake due to drinker allocation, Turner et al. (2000) concluded that conditions which increase the competition for drinker access such as a re-duced water flow rate, higher ambient temperature or a different feeding strategy, might still give rise to an effect of pig hierarchy, with subordinate animals being compromised. The results showed that the mean number of drinking bouts per pig per day was 30.9 (s.e. 1.41) visits/pig/day with a range of 7-98. It appears from the literature that increased competition to feeder access induce a higher ‘wa-ter/feed’ ratio. This could suggest that access to drinking water is generally subject to less constraint than feeder access, possible because of a higher intake rate. As stated in section 2.1 Yang et al. (1981) reported that pigs restricted in feed intake would take additional water, presumably to pro-duce feelings of satiety. With single space feeders, it appears that pigs in groups modify their be-haviour to adjust diurnal patterns of intake. Generally no adverse effects on life performance of the pigs have been seen with group sizes smaller than somewhere around 20-30 depending on housing


conditions, however Hyun and Ellis (2001) found contrasting results with smaller group sizes (sec-tion 2.3). Similar results were shown according to water access, however restrictions were less pro-nounced. As described are social factors according to group sizes an matters of competition often related to variations in diurnal patterns of feed and water intake in growing pigs. It is obvious that consistency in patterns of ‘water/feed’ ratio therefore would be susceptible to differing conditions between groups of pigs. This is in particular within shorter time intervals, as pigs tend to modify their behav-iour if restricted in access to feed or water according to competition.

2.4 Climate and light conditions In several studies climatic conditions have been found to strongly influence the eating and drinking behaviour of growing pigs. An interesting result reported by Walker et al. (1991) showed difference in ‘water/feed’ ratio between replicates (1.65 l/kg vs. 1.90 kg), however the study was mainly fo-cussed on aspects of competition as described in section 2.3.2. This difference in figures could sug-gest that climatic conditions (seasonal) or other aspects may have affected their results. As men-tioned in section 2.2.1 diurnal patterns of water and feed consumption are also highly related to cy-cles of light and darkness. Therefore it is relevant to focus on possible influences of climatic and lighting conditions, which we shall look further into in this section. Feddes et al. (1989) suggested that the general two peaks in feeder usage are primarily a response to light/dark pattern and the timing of the turning on and off the lights. Consistent with this statement Hyun et al. (1997) found only a single peak in feeder activity for pigs exposed to continuous artifi-cial lighting for 24 hours each day. The study of Young and Lawrence (1994) also showed a single peak in feeder activity for pigs housed in an open-fronted building where pigs were exposed to natural light and temperature levels. This trial was carried out during the months of November and December in Scotland. Acclimation to warm conditions mainly occurs by reducing heat production (Nienaber and Hahn, 1982; Quiniou et al., 2001). A general behavioural pattern seen in pigs exposed to higher ambient temperatures is panting. Collin et al. (2001) claimed that although panting seems to cause an in-crease in activity, the benefit (heat loss) probably outweighs the cost (heat production). It is self evident that water needs will rise with increasing temperatures and therefore changes in climatic conditions should be considered when analysing drinking and feeding patterns of growing pigs. To exemplify this, Ingram et al. (1980) studied groups of weaner pigs and single animals exposed to combinations of different lighting regimes and ambient temperatures. The pigs were kept in a spe-cially constructed soundproof room where the windows were blacked out and the artificial lighting was controlled. A total of 35 pigs (6-12 weeks old), including both males and females of the Large


White breed were used. The animals were housed singly or in groups of 4 in an insulation room. Feed was provided ad libitum in an open bowl. A timer turned on the lights in the room at 0600 H and off at 1800 H automatically. Continuous records were made of motor activity, feed intake and water consumption. The treatments were exposure to continuous light or a 12 hour light:12 hour dark (LD) cycle at a constant temperature of 25○C. However in one group of 4 pigs the LD cycle was combined with a change of ambient temperature such that the light period was at 35○C and the dark at 25○C. In the presence of a LD cycle groups of pigs were most active in the light and took most of their feed towards the end of the light period. Single pigs also tended to be more active in the light, but the rhythms were less marked, and one animal was most active during the dark period. In continuous light, rhythms of activity and ingestion tended to collapse after only a few days, par-ticularly in pigs that were kept by themselves. When the ambient temperature was increased to 35○C during the 12 hour light and decreased to 25○C during 12 hour dark, the pigs was most active in the dark. The pigs were more active during the dark (cooler) period and also ate and drank sig-nificantly more. An examination of the plot of hourly mean values confirmed the existence of this nocturnal habit. Diurnal variations were recorded; but they were vulnerable to alterations in envi-ronmental conditions. The activity with a LD cycle showed a well-defined rhythmic pattern with a period of approximately 24 hour. The corresponding pattern for continuous light, although still showing some slight visual evidence of peaks at 24 and 48 hour, was very much less regular as shown in figure 2.8.

Figure 2.8 Mean values for activity in each hour during LD cycles (solid line) and during continuous light (dashed line); bar indicated light on (Ingram et al., 1980).

The peak of feed intake was towards the end of the light period and the difference between the light and dark period was statistically significant. The pattern for water intake was very similar to that of feed intake in that the positive difference between consumption in the light and dark was significant in 3 of the 4 experiments. The rhythms in feed and water intake tended to dimish in continuous ligh-ting. It is important to notice the pigs in the participating in the study of Ingram et al. (1980) were younger than the finisher pigs used for data analysis in this study. Liang and Wood-Gush (1984) reported that the exposure to different light regimes lead to signifi-cant difference in the total number of meals per day. Feeding behaviour of 4 castrated boars was


studied over 24 hours using a photo electric cell and continuous recorder at four LW stages: 20, 40, 60 and 80 kg. Four castrated Large White x Landrace boars from the same post weaning group were used in the experiment. Two of the pigs were on continuous light and two were on 8.5 hour light and 15.5-hour darkness. Pigs kept under the 24-hour light regime had more meals than pigs in the 8 hour - 15.5 hour light-dark regime. Over the first 8-hour period of the day, the pigs on the short day length spent more time feeding, where LW did not affect this measure. The lighting regimes had no effect on feed intake, eating speed or the percentage of total time devoted to feeding. However, the differences between body-weight stages were significant (table 2.5). Furthermore, both pair showed a significant degree of synchronised feeding. Table 2.5 The effect of light treatment and live weight on feed intake, eating speed and the percentage of total time de-voted to feeding of pigs in 23.5 hours (Liang and Wood-Gush, 1984). Treatment Live weight 20 40 60 80 Average P-value Feed intake (kg) 1 (8.5 H light) 1.150 2.674 3.200 3.406 2.608 2 (24 H light) 1.314 2.384 3.298 3.195 2.548 N.S.

Average 1.232 2.529 3.249 3.300 Level of significance between LW stages, P<0.01 Eating speed (g/s) 1 (8.5 H light) 0.171 0.583 0.765 0.863 0.595 2 (24 H light) 0.279 0.627 0.867 0.123 0.744 N.S.

Average 0.225 0.605 0.816 1.033 Level of significance between LW stages, P<0.05 Percentage of total time devoted to feeding in 23.5 h 1 (8.5 H light) 8.3 6.4 5.0 4.8 6.1 2 (24 H light) 6.1 5.0 4.6 2.6 4.6 N.S.

Average 7.2 5.7 4.8 3.7 Level of significance between LW stages, P<0.01

It appeared that pigs kept in individual pens under one of the two light regimes might have changed their feeding behaviour, but the total feed intake was unchanged. The results showed that pigs housed singly tended to be most active during the period of light although they had less well-defined rhythms than pigs kept in groups normally have. Mount et al. (1971) investigated the voluntary intake of water by 24 groups of 3 to 6 Large White pigs (21-73 kg live weight) during a total of 48 periods lasting 3 to 12 weeks each in a large calo-rimeter equipped as a pen. The temperature was kept between 7 and 33○C and the pigs were fed at levels ranging from 42g feed/kg LW to maximum intake (ad libitum). In all series the higher tem-peratures were associated with higher rates of water intake, and in all series there were a marked day-to-day variation in water consumption. Analysis of the rate of consumption of water during the 24 hour period showed that it was at a minimum between 0300 and 0900 H, and at a maximum from 1500 to 2100 H. At 7, 12 and 20○C, in series with restricted feed access, a little water was consumed between 2100 and 0900 H, but at 30○C the water intake during this night interval was as much as 30% of the daily total. There therefore appeared to be little difference between 7, 9, 12 and


20 and 22○C in respect of water consumption, although there was considerable variation between groups of pigs at any one temperature. At 30 and 33○C, however, the intake of water was consider-able increased. The mean ‘water/feed’ ratios ranged between 2.1 and 2.7 at temperatures between 7 and 22○C, and between 2.8 and 5.0 at 30○C. The range of mean water consumption extended from 0.092 to 0.184 l/kg BW per day. The results showing a considerable variation in the daily water in-take between groups of pigs at any one temperature is highly relevant in relation to the focal aim of this study. Also the fact that daily levels of water intake was highly susceptible to high ambient temperatures gives rise to further attention. Feddes et al. (1988, 1989) investigated influence of high cycling temperatures on feeding patterns and performance of young growing pigs. The feeding behaviour and feed consumption of growing pigs (starting weight of 36 kg) were studied over a 6-day period while they were in 2 chambers, each housing 4 pigs. The temperature in one chamber was held constant at 33○C while the other cy-cled between a minimum of 26○C at 0530 H and a maximum of 40○C at 1400 H. In both treatments, the mean daily temperature was 33○C. The light schedule was 16-hour light (0500-2100 H) and 8-hour dark. Water and feed were provided ad libitum and each chamber had one feeder capable of accommodating 3 pigs. Water was available continuously from a nipple drinker mounted on a pen partition at the rear of each chamber. Feeding behaviour was monitored continuously on a video recorder while feed consumption was determined every 4 minutes from an electronic output from a feeder scale. The results showed that feed consumption and feeder usage in both treatments were primarily a response to the LD pattern with 2 peaks in feed intake; one at about the time the lights were turned on and the other shortly before the lights were turned off. Feeding activity appeared to be driven by light changes in the pen. For a constant thermal environment, the two 2 periods of peak feeding activity occurred near the time the lights were switched on or off. The effect of cyclic temperatures was to change the time between the peaks so that feed consumption coincided with the minimum temperature during the morning and evening period. The data indicated that photoperiod had a greater influence on diurnal feeding patterns than did temperature. However, there was also an interaction between light and temperature. The constant or cyclic temperature regimes did not influence the daily time spent at the feeder by 1, 2 and 3 pigs; mean ingestion rates and daily feed consumption rates. The results also showed no change in the feeding rate because of change in tem-perature. The pigs’ mean ingestion rates in the cyclic and constant temperature were 14 and 15 g/min, respectively. A study was also performed by Collin et al. (2001) to investigate the influence of different ambient temperatures on the feeding behaviour of young growing pigs. 30 Crossbred (Large White x Land-race) x Piétrain male pigs, castrated at about 14 days of age and weaned at 28 +/- 1days of age were used for the experiment. To assess the acclimation of pigs to heat stress, the effects of high (33○C) or thermo neutral (23○C) constant temperatures on feeding behaviour and components of energy balance were studied in group-housed young pigs. During four days before the data collection


started the temperature was progressively adjusted from 25○C to the treatment temperature. Three periods (days 2-5, 7-9 and 10-12) were distinguished, to account for the rapidly changing LW of the pigs during the experimental period. The results showed that BW gain and voluntary feed intake (VFI) were reduced by 37% and 30% respectively at 33○C. The decrease in VFI corresponded to reduced consumption time (-34%) and size of meals (-32%). Feeding behaviour was mostly diurnal (66% of the VFI), and the rate of feed intake (28 g/min.) was not affected by temperature. VFI was reduced at 33○C, being 30% lower than at 23○C with subsequent lower BW gain at 33○C than at 23○C (621 vs. 987 g/d). In addition, feed conversion ratio (FCR) was significantly lower at 23○C than at 33○C (1,50 vs. 1,68). Despite the lower feed intake, there was a tendency for increased water consumption at 33○C. The average VFI was reduced from 1,483 to 1,045g/day, whereas voluntary water intake was increased from 4,408 to 5,863 ml/day, by the increase in temperature from 23○C to 33○C. This change in figures equals an increase in ‘water/feed’ ratio from approx. 2.97 to 5.61 l/kg. The comparison of results obtained at 23 and 33○C indicates that VFI declined by 45g/○C, which is similar to the 42g/○C calculated from an earlier study of Sugahara (1970) who studied young pigs when exposed to different temperature regimes (7, 23 or 33○C respectively). In the experiment of Collin et al. (2001) pigs were housed in groups, which may have stimulated feed intake, at least at thermo neutrality. In addition, the relatively high BW gain and VFI recorded at 23○C, the tempera-ture of 33○C could also have induced accentuated effects of heat exposure. The temperature did not seem to affect the daily number of meals, which was consistent with results of Quiniou et al. (2000), also obtained in group-housed animals. It appears as a result of heat stress that heavier pigs shift a part of their meals to the night, which has been described in studies with cyclic temperatures mimicking real daily temperatures (Feddes et al., 1989; Xin and De Shazer, 1991). Xin and De Shazer (1992) investigated feeding behaviour of ad libitum-fed, 39 kg, crossbred gilts under mean ambient temperatures of 30.8○C with 0, 7, and 16.6○C cycles. The focal aim was to in-vestigate the influence of high ambient temperatures (>30○C) at different times according to light regimes. The treatments were: CON: simulated constant temperature of 30.8○C, RPK: reduced day-time peak temperature cycling from 26 to 33○C (mean 30.8○C), and RNT: reduced nocturnal tem-perature cycling from 23.4○C to 40○C (mean 30.8○C). Daily feed intake of the pigs was significantly less in the 16.6○C cycle treatment than in the 0○C and 7○C cycle treatment. Feed consumed during the lighting period (0600 to 2100 H) accounted for 75%, 61%, and 37% of daily intake for the 0, 7, and 16.6○C cycle treatments respectively. Pigs under the 0○C cycle had most feeding activities in the afternoon and evening (55% of daily intake). In contrast, pigs under the 16.6○C cycle had most feeding events at night and early morning (91% of daily feed intake). The CON pigs had most feed-ing activities in the afternoon and evening (between 1500 and 2100 H), consuming 55% of their daily feed intake. These pigs showed a gradual increase in their feeding activity till darkness. In contrast the RNT pigs had most feeding events at the cooler night and early morning (between 2100 and 0900 H), with 91 % of their daily feed intake. In spite of the increased feed intake by the RNT pigs during the cooler period, it was not enough to fully compensate for the feed intake depression


from the high temperatures. By comparison, two peaks of feeding activity featured hourly feeding profile of the RPK pigs. One peak was in the evening and the other was from late night to early morning (fig. 2.8).

020406080100120140160180200

12 14 16 18 20 22 0 2 4 6 8 10

Time of day (hour)

Feed

inta

ke (k

g/ho

ur/p

ig)

CONRPKRNT

Figure 2.8 2-hourly feed intake of growing pigs under the simulated constant temperature (CON) of 30.8○C; reduced day time peak temperature (RPK) cycling from 26○C to 33○C with mean 30.8○C; and reduced nocturnal temperature (RNT) cycling from 23.4○C to 40○C with mean of 30.8○C (mod. a. Xin and De Shazer, 1992).

The stimulating effects of lighting on feed intake were shown by the 61% and 75% of daily feed intake that occurred during the 15-h lighting period for the RPK and CON pigs, respectively. How-ever, the concurrent high temperature overwhelmed the effect of lighting and thus normal feeding rhythm was disrupted in the RNT case. We will now change focus to pig’s exposure to extreme lower temperatures, to find out possible consequences on water intake and feed intake. Performance data from Nienaber et al. (1990) showed that cold stressed pigs ate slower than pigs at thermo neutral temperature. Cold-stressed pigs compensated by eating more frequently and consumed more feed per unit LW although meal size was not affected by temperature. In the study feeding behaviour of 21 crossbred gilts from 28 to 103 kg live weight were examined. The pigs were selected at weaning (28 +/-2 days of age) and averaged 8.7+/-1.0 kg. 7 pigs were assigned to individual growth pens (1.2m x 1.2m) in each of 3 controlled environment chambers. The temperature was maintained at 30○C for the first week after weaning and lowered to 24○C for the second week. Thereafter, treatment temperatures were estab-lished on the basis of the average calculated LCT for all pigs with adjustments made every second week. LCT is the Lower Critical Temperature as defined by Bruce and Clark (1979). LCT depends on the animal’s LW, floor type, air speed, number of pigs per pen and daily feed intake. The cold-stressed pigs required more feed per unit of gain and subsequently lost a greater amount of heat per unit BW. Environmental temperatures of LCT-4○C and LCT-12○C caused respective 8.6 and 18.9% reduction in gain, while feed intake adjusted for LW increased by 14.8% and 29.6%, compared to the control treatment (LCT+4○C). The number of daily meals was highest for the LCT-12○C treat-ment. The rate of feed consumption decreased at the LCT-12○C treatment while the eating rate did


not differ between LCT-4○C and LCT+4○C. Feed conversion ratios averaged 2.75, 3.14, and 3.72 kg feed/kg gain, for LCT+4○C, LTC-4○C, and LCT-12○C, respectively. Average heat production increased at an average of 7.13 Kcal/d/○C /kg0.75 as temperature decreased from the control to the LCT-4○C treatment. There was also a reduction in heat production per kg0.75 with age. Like figure 2.9, the growth curve was linear, indicating normal growth for the control treatment over the 11-wk period.

Figure 2.9 Changes in live weight for pigs in the control group (LCT+4ºC) (Nienaber et al., 1990).

As described in chapter 2.2.2 Turner et al. (1998, 2000) investigated the drinking pattern of growing pigs and the influence of drinker allocation to different group sizes of pigs. Although, the mean daily temperature ranged from 14.3 to 18.2○C over the four replicates no significantly influence of the drinking patterns was observed. The four replicates were allocated sequentially between January (replicate 1) and July (replicate 4). It is apparent from the results described in literature, that light and temperature have a strong influ-ence on characteristics of feed and water intake patterns of growing pigs. In particular single penned pig appeared to be most active during light hours, however light regimes did not affect total daily intakes of feed. Light seems to have greater influence on diurnal patterns of water and feed con-sumption than does temperature, however extreme high temperatures can overwhelm the general effect of light patterns. In situations with extreme high temperatures feed intake, and LW gain was generally decreased whereas water consumption was increased significantly. The decrease in daily feed intake was generally a response to shorter visits, as the number of daily meals was unchanged with higher temperatures. Extreme lower temperature (<LCT) appeared to increase feed intake and decrease LW gain. In this situation feed intake was increased by a higher meal frequency while meal size was unchanged. Impacts on water consumption were not reported. The results just de-scribed indicate that seasonal variations associated with changes in temperature or light patterns could have an impact on the patterns of ‘water/feed’ ratio in growing pigs. Similarly diurnal pat-terns and levels could also be influenced by climatic variations according to allocation of windows, provision of artificial light, ventilation and central heating systems, etc.


2.5 Other factors As we have seen in the previous sections several conditions and factors seems to have influence on drinking and/or feeding patterns in growing pigs within a shorter or longer time intervals. It is obvi-ous that physical factors in the near environment play a role in relation to social behaviour and competition between group members. Therefore to expect similarity in such behavioural patterns between groups of pigs, similarity in housing conditions is necessary. Other factors are those as de-scribed in the previous section according to lighting and climate conditions. 2.5.1 Housing conditions When discussing housing condition’s influence on feeding and drinking patterns of growing pigs, central aspects are, space allowances, feeder access, drinker access and climatic conditions. Even smaller differences might cause variation between groups, which could affect the ‘water/feed’ ratio. As stated in the introductory chapter estimation of water requirement for growing pigs is difficult. Whittemore (2000) exemplified it, as the means of providing free availability to water is a more ap-propriate subject for systematic study than any factorial estimation of requirement. The presence in the pen of a water point, in the form of a through, bowl or nipple drinker, may not be taken to imply free availability. Therefore careful siting of water points, and maintenance of adequate flow rate are necessary (Whittemore, 2000). Nielsen et al. (1996A) investigated the effect of single space feeder entrance design on the perform-ance and feeding behaviour of growing pigs. The experiment was carried out with three replicates of 90 entire male pigs from a starting weight of approx. 34 kg allocated in groups of 10 to pens. The pens contained one of three different feeder entrance designs providing various degrees of protec-tion whilst eating. The results showed that access to a feeder with low protection resulted in a faster eating rate. Nielsen et al. (1996A) suggested that this faster eating rate could indicate that pigs using the low protection race were more disturbed during feeding. The feeders with higher degrees of pro-tection were also the most difficult to enter, and therefore it was also suggested that the decreased accessibility to the feed may have resulted in similar changes in feeding pattern to those seen with increased competition. Apart from design affecting patterns it can also influence the specific levels recorded, as waste of water or feed are often included in measurements. A specific example is difference between using nipple drinkers or closed type drinker bowls. A study of Petersen (1995) showed that closed water bowls rather than nipple drinkers reduced water expenditure by approx. 30% in pigs growing from 45 kg to 100 kg. As an average for the entire test period ‘water/feed’ ratio was reduced from 3.7 l/kg to 2.4 l/kg of dry feed. In a similar study described by Smidth (1990) a smaller decrease in ‘wa-ter/feed’ ratio was found, as figures was reduced from 3.1 to 2.8 l/kg dry feed.


As a supplement to the results of Turner (2000) (section 2.3.2), Whittemore (2000) claimed that one water point is needed for every eight pigs in a pen, this ratio covering all pig types from growers to adult sows to ensure free access at any time. General Danish recommendations for drinker alloca-tion to growing pigs are a maximum of 10 pigs per nipple drinker, however if closed bowl type drinkers are used no more than one per pen is recommended, as pigs will often use excessive drink-ing bowls for defecation rather than drinking (Smidth, 1990). It is clear from the examples given that differences in design of housing facilities can either directly or indirectly affect levels and patterns of feed or water intake recordings in pigs. 2.5.2 Feed composition As described in the introduction of this chapter animals obtain water from three sources: drinking water, water present in the feed and metabolic water. Growing pigs’ requirement of drinking water is very dependent on content in the pigs diet and also the specific composition of nutritional com-ponents play a role (McDonald et al., 1995). Water output is increased in proportion to the level of dietary un-ideal protein and dietary protein excess consequent upon the need to dilute the deamina-tion product (urea) to a level of concentration appropriate for urinary excretion (Whittemore, 2000). To stabilise water balance such shortage will initiate thirst and increase water intake by the animal (Reece, 1997). Other factors in the diet affecting water needs are also content of salts of Na and K as they play a central role in ionic balances (Whittemore, 2000; Reece, 1997) Differences in specific feed compositions allocated to animals within or between groups is likely to cause variation in the patterns of water and/or feed consumption. Water content of feeds is very variable and can range from as little as 60 g/kg in certain concentrates to over 900 g/kg in some root crops, e.g. barley grain contains approximately 140 g water pr. kg (McDonald et al., 1995). 2.5.3 Health conditions (diseases) Health conditions of the growing pigs may play an important role regarding water and feed intake patterns, and symptoms would also vary depending on specific types of medical conditions. It is not a focal aim of this study to investigate how diseases affect water and feed intake, however to ana-lyse ‘normal’ situations it is useful to have information about consequences in general, to be able to exclude invalid data from the analyses. Most commonly diseases such as types of diarrhoea are con-sidered to affect water balances in a negative way, thus disrupting normal patterns of both water and feed intake. The consequences of diarrhoea are those of water shortage due to uncontrolled faecal losses, and dehydration of the essential tissues. This leads to disruption of ionic balance and failure of the endogenous biochemistry to operate in the absence of an adequately fluid medium (Cunningham, 1997; Whittemore, 2000). As the sick animal will try to compensate for such imbal-ance, water intake especially is considered to be increased however rehydration requires not only water, but also appropriate electrolytes (Reece, 1997). Outbreaks of influenza, pneumonia or other


common diseases is generally expected to have a decreasing effect on feed and often also water in-take, however patterns vary and are subject to variation (Nielsen et al., 1976). 2.5.4 Human activity It is possible that human activity can affect feeding or drinking behaviour of growing pigs in both positive and negative ways. In the study of Nienaber et al. (1990) as previously referred approxi-mately 14% of the total daily feed was consumed from 0700 to 0900 H, immediately after feeders and drinkers were replenished and when most of the human activity occurred. It is possible that the activity and the replenishment of feeders and drinkers stimulated intake, but at the same time diur-nal patterns are usually correlated with patterns of daylight. In contrast approximately 25% of the feed was consumed from 1300 to 1600 H, when there was a minimal amount of human activity, but this time of the day is also usually coincident with peak hours of the well recognised bimodal pat-tern as previously described. Whether human activity in the building has a positive approach to animal performance or should be considered as a disturbance is very much dependent on the animals usual contact with humans. Characteristics such as duration and intensity of the human activity also play a role (Fraser and Broom, 1995). When analysing drinking or feeding patterns attention on odd incidences of human disturbance may need to be paid. Specific examples are such as medical treatments (i.e. injections), or just general task as mucking out, bed spreading, observing, weighing, etc. It is apparent from aspects described in this section (2.5) that several factors in the near environ-ment can affect patterns and levels of water and feed consumption in growing pigs. This is accord-ing to housing conditions, feed composition, and human contact. Therefore to expect similar pat-terns of the ‘water/feed’ ratio between groups of pigs, housing conditions, feed offered, human con-tact etc. must be similar. Regarding physical facilities and housing conditions is it obvious that mat-ters of those would affect patterns as they are closely related to climatic and social conditions. Dis-eases can strongly affect water and feed intake, and consequently awareness of medical conditions is also important.

2.6 Breed and sex Studies have shown some variation in the feeding patterns of pigs related to difference in breed and sex. Puberty of females normally does not occur within the life range of slaughter pigs, as it gener-ally happens at ages in excess of 190 days and in excess of 100 kg LW (Whittemore, 2000), al-though it may occur at 5 months of age (Thorup, 1992). It is generally understood that pigs in oes-trus show a decline in feed intake (Whittemore, 2000), which would affect eating patterns between different groups of pigs. A manual count in 1990 on the slaughter line in a Danish abattoir showed that approx. 10% of female pigs was cyclic (Thorup, 2003). Therefore it is likely that female pigs


for slaughter could change patterns of feed and possible water intake at the end of their life period, which could violate general levels of ‘water/feed’ ratio. Boars generally convert feed more efficiently than gilts or castrates, whereas castrates grow signifi-cantly faster due to a higher feed intake (Cole and Haresign, 1985). From a study Haer and Vries (1993) reported that Boars had less visits and meals per day, but they had a higher eating time per meal compared with gilts. A study of Hyun et al. (1997) showed that differences in feeding patterns among boars, castrated males, and gilts in mixed-sex groups were relatively small. Castrated males had greater number of meals per day than the other two sexes (7.4 vs. 7.0 +/- 0,10 respectively), however, the sex difference were small and there was little influence of sex on the other feed intake traits such as total daily intake. These results was contrasted by Labroue et al. (1994) who found that castrated males ate more per day than boars in a trial with 420 pigs of both Large White and French Landrace. The pigs in this trial were raised from 35 kg to approximately 100 kg. Eating time of the castrated males was longer both per meal and per day and their daily feed intake was higher by 367 g i.e. 17 %. On the other hand, the study showed no difference either in the number of feeder visits or meals per day, or in the rate of feed intake between castrated males and boars. In contrast to the variation found in feeding patterns according to the sex of pigs, there also appears to be a variation related to differences in breed. The study with boars and castrated males of two different breeds by Labroue et al. (1994) also showed difference between breeds especially regard-ing diurnal feeding patterns. Large White performed twice as many visits per day as French Land-race pigs, but daily feed intake was the same in the two breeds under both housing type conditions (single breeds or mixed breeds). Table 2.6 summarises selected result of Labroue et al. (1994) on the behavioural traits between French Landrace and Large White pigs and between boars and cas-trated males of the two breeds. Table 2.6 Analysis of variance of behavioural traits (significance levels) (mod. a. Labroue et al., 1994). Trait Breed Sex1) Number visits/day P<0.001 N.S. Feed intake/meal (g) P<0.001 P<0.001 Time per meal (min.) P<0.001 P<0.001 Number meals/day P<0.001 N.S. Feed intake/day (g) N.S. P<0.001 Eating time/day (min.) N.S. P<0.001 Rate feed intake (g/min.) N.S. N.S. 1) Sex refers to whether the pigs were entire males or castrated males.

It is apparent that variations in the behavioural patterns differed within each of the two analyses per-formed by Labroue et al. (1994), however total amounts of feed intake most importantly varied be-tween castrated males and boars.


Musial et al. (1999) found in a trial with Munich minipigs (29-52 kg/6-9 months old) that this breed were nearly as active during the night as during the light cycle. These animals ingested approx. 50% of their daily energy intake during the dark cycle, which was surprising as pigs are considered to be most active during daylight, with most of their feed intake occurring during this time (Ingram et al., 1980, 1985). Musial et al. (1999) observed that the diurnal behaviour of Munich minipigs is similar to that seen in wild pigs, suggesting that this particular breed is closer to the wild form than Large White or Landrace. The results found by Musial et al. (1999) are not comparable to general condi-tions of domestic pigs, but they suggest that behavioural traits affecting diurnal feed and water in-take can be associated with the genetics of the individual animal. Daily feed consumption is different between sexes of pigs as in particular castrated males consume more than gilt or boars. There is some indications that patterns of feed and water intake in older fe-male slaughter pigs could be affected by cycling sows, however this is not considered to play a ma-jor role within groups of slaughter pigs. Difference in breed seems to influence diurnal patterns whereas differences in total daily amounts are marginal. Information on water consumption accord-ing to sex or breed has not been found.

2.7 Chapter summary Diurnal patterns of feed and water intake in growing pigs are distinct, generally with one or two daily peaks as a primary response to light and darkness. The literature reviewed has shown that pat-terns are highly dependent on the state of the individual animals (i.e. age, sex, breed) and also envi-ronmental factors (i.e. climatic and lighting conditions). Table 2.7 summarises important factors that affect daily levels and diurnal patterns of water and feed intake as shown by the literature. The factors shown in table 2.7 are not a complete list, however they are representative of examples. Some of these factors are secondary causes, as they are a response to other factors of a more pri-mary nature (e.g. housing facilities can affect competition levels). In section 2.5.1 we saw that hous-ing conditions could affect the measurements of water and feed consumption indirectly or directly. An example of an indirect condition was the measurement of water or feed spillage according to the differences in design of feeders or drinkers. An example of a more direct condition was that the feeder entrance design influenced competition between individual pigs.


Table 2.7 Summary of factors affecting patterns of water and feed intake in growing pigs according to the literature review in this chapter. (Yes=effect, No= no effect, ‘↑’=increase, ‘↓’=decrease, ‘-‘ = effect not clear/not investigated). Factors Water intake Feed intake ‘Water/feed’

ratio1 Daily levels

Diurnal patterns

State of animal Age (increasing) Yes (↑) Yes (↑) - Yes (↑) Fewer but larger meals

Sex - Yes - Yes Yes Breed - - - - Yes Competition Yes Yes Yes Yes Yes Temperature Extreme higher Yes (↑) Yes (↓) Yes (↑) Yes Yes Extreme lower - Yes (↑) Not clear Yes (↑) Yes Light patterns Yes Yes Yes No Yes Feed Composition Yes Yes Yes Yes No Health Diseases Yes (↑↓) Yes (↓) Yes (↑↓) Yes - Human activity Stimulating Yes (↑) Yes (↑) - Yes (↑) Yes Disturbance Yes (↓) Yes (↓) - Yes (↓) Yes 1) Whether patterns or levels of the ‘water/feed’ ratio are affected by factors listed in the table is highly dependent on the time interval of observation, this in particular when diurnal patterns are also affected.

Feed and water intake are also dynamic responses, which can be influenced by thermal environ-mental conditions and exposure to different lighting regimes. Generally photoperiod has greater in-fluence on diurnal patterns of feed intake than does temperature. However it appears from studies, which have analysed combinations of extreme temperatures, that concurrent high temperatures overwhelmed the effect of lighting and thus normal feeding rhythm was disrupted. Generally tem-peratures deviating strongly from the pigs’ comfort temperature are expected to influence the gen-eral patterns and levels of water and feed consumption. Lighting regimes mainly affect diurnal pat-terns, whereas the total levels of daily consumption are less affected. Differences between breeds are expected to affect diurnal patterns of feed intake, however total daily intake does not seem to be subject to similar variation. Review of the literature also showed that differences between breeds are expected to affect diurnal patterns of feed intake, however total daily intake does not seem to be subject to similar variation. Of note also, is the fact that the amount of feed consumed by castrated males is higher than that of gilts or boars. Following from that, and described in section 2.6, oestrus pigs could be expected to cause variations in patterns of feed and water intake. However, the effects of this are not clear and the impact would only affect a certain percentage of pigs at the final growth period. Whether the ratio between water and feed consumption on a day-to-day basis is characterised by a constant level according to the age of the pigs, or whether it is associated with some change in level over time is not quite clear, although an older study by Pieterse (1963) reported a declining pattern. It appears that the shorter time intervals are considered, the more attention needs paying to tempo-rary conditions affecting the ‘water/feed’ ratio. Thus, the literature indicate that patterns of ‘wa-ter/feed’ ratio in growing pigs would be very variable between time intervals shorter than at least 24 hours. This is because diurnal patterns are highly susceptible to conditions in the near environment of the animals. Should a similar pattern between groups of pigs (i.e. in different housing sections)


be expected, then all physical facilities and conditions must be identical. This is due to the fact that social behaviour and competition between pigs within groups are highly susceptible to constraints caused by differences in housing conditions; e.g. feeder or drinker allocation. Social constraints lead to significant increases in the feeding rate and diurnal patterns are commonly recognised as being affected also. In ‘practical’ animal production systems, conditions between groups of pigs cannot be considered as being identical in all facets as necessary. Therefore the results in this chapter suggest that it would be most appropriate to give attention to daily records of ‘water/feed’ ratio. Similarly, if ana-lysing data from practical conditions attention must be on relevant factors influencing on daily lev-els (and long term patterns) of water and feed consumption. Thus, central points from this chapter are used to select suitable parameters for the data analysis in the following chapter. The findings from literature have then been used to evaluate the results and make final conclusions regarding the ‘water/feed’ ratio in growing pigs.

Chapter 3 Experimental study 31 ________________________________________________________________________________

3 Experimental study (field data with slaughter pigs) In this chapter data obtained from a central testing facility (Bøgildgaard) in the Danish breeding program has been used to analyse patterns of ‘water/feed’ ratio under practical conditions. In order to investigate the relationship between levels of water and feed intake, consumption curves were analysed separately along with the combined ‘water/feed’ ratio. The primary reason for studying water and feed consumption separately was to investigate whether possible variation in the ‘wa-ter/feed’ ratio was due to variation in water or in feed consumption. This chapter is divided into three sections, where the first section describes the general conditions from which data have been collected. The second section describes preliminary data analysis and methods applied in the process of analysing data. As described in the previous chapter, to expect consistent diurnal patterns of ‘water/feed’ ratio within and between groups of pigs would require similar and standardised conditions between groups. According to the literature it would therefore not be relevant to focus on time intervals shorter than a day length. However, as conditions were considered to be identical between the pens (in the same housing section), further attention towards this topic was paid as part of the preliminary data analysis. The third section of this chapter contains final models and brief results from the data analysis performed. 3.1 Materials At the testing facility boars were kept within a strictly controlled environment with specific registrations of feed consumption, medical treatments, possible disease problems, and other factors considered to influence performance of the animals in their manifestations of life. The data used was generally collected for purposes of testing, selection and improvement of genetic material in Danish Pig production. Therefore conditions must be considered as well managed field facilities rather than a trial set up solely for the purpose of this study. Nevertheless data were found useful for this project as data was collected with a high velocity, although some parameters of interest were not recorded. The data analysed were collected during a period of approx. 1½ years with 670 pigs allocated on 6 batches as shown in table 3.1.

Table 3.1 Batch periods. Batch no. Period

1 13.09.2000 – 19.12.2000 2 30.01.2001 – 08.05.2001 3 22.05.2001 – 29.08.2001 4 17.09.2001 – 12.12.2001 5 03.01.2002 – 10.04.2002 6 23.04.2002 – 31.07.2002


3.1.1 Pigs The pigs were all pure breed boars of Duroc, Hampshire, Yorkshire (Large White) and Danish Landrace. The piglets were sent to the controlled test environment at weaning. When the boars reached a live weight of 24 kg (approx. 10 weeks) they were transferred to the experimental hous-ing facility and grouped 14 into each pen (8 pens in total). The pigs were not mixed between groups at the time of insertion to the experimental housing conditions. Under the prehousing conditions the pigs were vaccinated following a strict strategy, which will not be described in detail here. How-ever, the 3rd vaccination for Pneumonia was not practised until approx. 7 weeks after insertion into experimental housing facility. Trial registrations were terminated at slaughter (approx. 100-105 kg live weight). The general distribution of different breeds was as shown in table 3.2 and specific breeds very generally allocated to the same pen numbers between batches. Additionally in some batches one pen contained mixed Hampshire and Duroc boars. Table 3.2 Common distributions of different breeds in each section.

Breed Number of pens (pigs) Duroc 3 (24)

Hampshire 1 (8) Yorkshire 2 (16) Landrace 2 (16)

This allocation of breeds between pens with lack of randomisation caused some problems in the data analyses as further discussed in section 3.2. 3.1.2 Housing conditions The test station had 16 identical house-sections with 8 pens, where one section additionally had been equipped with a water monitoring system (FarmWatch) as described by Madsen (2001) on pen level. Data used for this study was collected from this particular house section. The houses were built in 1981. The boars were fed ad libitum, and in order to monitor the feed intake of each pig in-dividually, the testing facility was equipped with ACEMA-48 single space feeding stations (ACEMA, 2002). The manufacturer claims that the feeders have an accuracy of +/- 2 g per visit. Data on the feed consumption for the individual pigs were electronically recorded and stored into a central database, together with the identity of the pig concerned. Identity of the individual pig was electronically recognised by an ear tac. The design of the feeding station allowed only one pig at the time feeding, as a gate closed behind the pig as it entered. Feed data were stored each time a pig vis-ited the feeding station with recordings of the consumed amount, time of entrance and time of leav-ing the feeding station. Figure 3.1 illustrates the general design of the pens. Each pen had a space of 13.0 m2

+ 1½ m2 for the feeding station, yielding a space allowance of approx. 1.0 m2 per pig with 14 pigs in each pen.


Figure 3.1 Design of the pens (measurements in metres).

All pens had non-slatted floor, and removal of manure was performed manually. A single closed bowl type drinker (Suevia, 2002) was located at the centre on the front side of the pen (approx. 3 m away from the feeding station). Data recordings of water consumption on a pen level were stored in a separate FarmWatch database as hourly totals. As mentioned in the introduction chapter Farm-Watch is originally designed for detection of deviations in diurnal patterns of water consumption related to health problems in growing pigs (Madsen, 2001). The FarmWatch system is generally used on larger groups of animals (e.g. housing sections) with water meters providing one electronic signal per litre of water consumed. However, for the purpose of use on pen level water meters of higher accuracy were chosen, as these provided 150 electronic impulses per litre of water consumed instead (Digmesa, 1999). The outlay of the building was a design with 4 pens on each side of the inspection path as shown in figure 3.2 and 4 windows placed evenly along each side of the building.

Figure 3.2 Outlay with 8 pens in the building (pen nos. and general distribution of breeds: Yorkshire (Large White), Landrace, Hapshire and Duroc).

From 0600 - 1800 H the building was illuminated with artificial light, and in order to stimulate feeding activity a single fluorescent light was turned on during the hours of darkness. The climate in the building was controlled with a mechanical ventilation system having 2 roof extraction units and


18 inlet valves placed evenly on the outer wall at both sides of the building (vacuum system). The inlet valves were model ‘FP 700’ from Funki delivered in 1981. The extraction units were an older Funki type upgraded with modified fans and motors (model 520 M) supplied by the company TH Klimateknik in 1992. Each extraction unit had an estimated maximum capacity of 5.500 m3/h, wheras each inlet valve had a estimated capacity of 500-550 m3/h (Nielsen, 2003). Additionally, twin pipes for central heating were installed under the inlet ventilation valves, to ensure sufficient ventilation particular at lower outdoor temperatures. A temperature curve program was used, gradu-ally to lower the temperature from 22°C to 18°C during the growth period of the pigs. The control unit was a model TH-41 supplied by TH-Klimateknik in October 2000 (start batch no. 1). Humidity control was used in combination with temperature regulation. The system was generally susceptible to extreme outdoor conditions, so that particularly high summer temperatures could be expected to affect the indoor climate with deviations from the desired conditions. Therefore, particular at warmer seasons of the year diurnal climatic variations could be expected. 3.1.3 Feed, bedding material The feed supply used was a standard but high quality cereal-soya based pellet diet added organic acids (Hedegaard, 2002). The full meal mixture was used for the entire period in the experimental housing conditions. Barley straw and wood shavings were allocated daily to provide bedding mate-rial. 3.1.4 Working procedures, registrations, data logging, medical treatments, etc. Human activity began at 0700 H in the morning hours with mucking out and other daily jobs. Bed-ding was usually spread between 0900 and 1100 H. Registrations of vaccinations, medical treat-ment, diseases, removed animals, etc. was stored in a logbook at the same database as the feeding activity was recorded. All data recordings were done carefully to insure a high information level about the individual pigs in trial. Generally the same employee did the daily tasks in the building to ensure homogeneity in the daily working procedures. A weekly recording of live weight was made, and scans (not used in this study) of backfat thickness at the P2 location was performed one week before slaughter. Ordinary registrations of such as medical conditions, treatments and pig removals were stored in the database with a code system referring to the pig identity concerned. 3.1.5 Preparation of data A focal aim of this study was to examine water and feed intake patterns over time between groups of pigs. As recordings of water consumption were performed on pen level with 1-hour sums, the feed data were also accumulated as sums within the hour of entrance to the feeding station. Tables in appendix 1 show recordings from the logbook data, which appeared to have violated or affected daily levels of either feed or water intake to such an extend that data have been excluded from the analyses (see section 3.2.1 for further detail). All data were stored in ASCII text files except the wa-


ter data that was stored in an ACCESS data file. All data files of interest for this study were read by data steps created in SAS. 3.1.6 Limitations Pure breed pigs at the experimental station were kept within a strictly controlled environment as described. The use of these strictly controlled facilities mean that the results of this study are not necessarily transferable to pigs kept in housing conditions of any type. Another limitation is that the study primary involves and describes pigs that have been fed on dry feed diets with relatively low water contents, approx. 13.5% (Maribo, 2002). Any situations with medical treatment affecting patterns have been excluded from the analyses, as diseases have not been properly diagnosed in the animal herd. Therefore the results only represent normal situations without health problems. Conse-quently such limitations play an essential role in the discussion and overall evaluation of results ob-tained from this study. 3.2 Preliminary data analysis Validation of data and choosing an appropriate statistical method for analysing data are central points of this section. Firstly a provisional investigation of the development in the ‘water/feed’ ratio during the growth period of the pigs was performed. An analysis of the pattern regarding ‘wa-ter/feed’ ratio was expected to be more robust in situations with removal of a single or few pigs from a group than separate examinations of water or feed curves. As discussed in chapter 2, pigs are considered to be prandial drinkers (e.g. Ingram et al. 1985; Houpt, 1985) which means that a change in the number of pigs within a group would be expected to cause a similar change in the absolute levels of both water and feed intake simultaneously. Analyses of separate curves of water and feed consumption would therefore also be more susceptible to a change in the number of animals. The analysis of single curves of water or feed intake would therefore need more attention as the removal of pigs at an arbitrary time within a 24-hour day would affect the pattern of consumption per pig, however, the combined ratio is also of most interest for this study. 3.2.1 Data validation The first step in the process was data validation to ensure that only data from ‘normal’ situations was being included. ‘Normal situations’ are defined as situations where regular patterns of ‘wa-ter/feed’ ratio, water or feed consumption have not been violated by medical conditions, removal of pigs, habitation period, etc. Data validation was performed by (explorative) examinations of the raw data and comparing this to registrations in the logbook as listed in appendix 1. Although the aggregate method (’water/feed’ ratio) was considered to be quite robust to changes of group size, certain parts of the data series have been excluded from the analyses. Diagrams in ap-


pendix 2 show plots of daily water and feed consumption per pig and ‘water/feed’ ratio before man-ual exclusion of invalid data. However, data obviously invalid has been excluded. Because of the habituation period the young pigs had to a new environment (and new feed), data from approx. the first week after moving into the building has been excluded. At the end of the growth period when pigs were starting to leave the building, an approximate criterion of five pigs per pen was also practised to ensure a certain degree of homogeneity in the feeding and drinking behaviour according to competition levels. Unfortunately recordings of the water consumption were disrupted by several technical failures dur-ing the period of observation. As water data collection was considered to be a low priority from a managerial point of view, recurrent system failures have not been observed and repaired with the same velocity and care as the feed monitoring system was. This led to a considerable loss of data. Figure 3.3 shows the mean levels of ‘water/feed’ ratio between batches prior to exclusion of invalid data. Maximum values for batch no. 3 and 4 are not shown in the diagrams as they represented val-ues as high as 39 and 53 respectively.

0

2

4

6

8

10

0 1 2 3 4 5 6

Batch no.

'wat

er/fe

ed' r

atio

W/F mean

Max.

Min.

Figure 3.3 Mean levels of “Water/feed’ ratio between batches.

Figure 3.3 shows a variation in the mean levels of the ‘water/feed’ ratio between batches. After re-moval of invalid recordings according to failure in the water monitoring system a better stability in figures appeared. Figure 3.4 shows the development over time of the ‘water/feed’ ratio on a daily basis during the growth period of pigs from batch no. 1 in pen no. 1-4. A relatively stable pattern appeared in all data series, although some variation was observed between batches and pens.


Bat ch no. 4

pen 1 2 3 4

1

2

3

4

5

6

day

0 10 20 30 40 50 60 70 80 90

Figure 3.4 Development of the ‘water/feed ratio’ during the growth period of pigs belonging to batch no. 4 and pen no. 1 to 4.

Figure 3.5A shows a plot of ‘Cook’s distance influence statistics’ after the first validation of data, revealing relatively strong influencing data from several observations, particularly in batches no. 3 and 4. The plot is made from data where observations existed with 24-hour valid water data. It should be noticed that the model behind this analysis was a simple General Linear Model (GLM), not fully identical to the more advanced Mixed model applied in the later analysis of the ‘wa-ter/feed’ ratio. The GLM model behind was a simple covariate model that only considers fixed ef-fects (see appendix 3 for further detail).

d

0. 00

0. 01

0. 02

0. 03

0. 04

0. 05

0. 06

0. 07

0. 08

0. 09

0. 10

Bat ch

1 2 3 4 5 6

d

0. 00

0. 01

0. 02

0. 03

0. 04

0. 05

0. 06

0. 07

0. 08

0. 09

0. 10

Pen

1 2 3 4 5 6 7 8

Figure 3.5A and B Cook’s distance influence statistic plots before and after removal of invalid data. Notice that the first plot is based on batch levels whereas the second one is based on pen levels.

As a general rule values higher than 1.0 are considered to be of significant influence on the accu-racy of the results and require conscious awareness (Bibby, 2001). As can be seen in figure 3.5A, no values were higher than 1.0 and therefore none need consideration. However it was decided to lower the threshold (to 0.02) due to the fact that this model was simpler than the following models, and a higher uniformity of data was desired. This further exclusion of invalid data was also per-formed while comparing to the logbook registrations. Figure 3.5B shows the diagram of ‘Cooks in-fluence statistics’ after removal of this invalid data.


The poor data quality regarding water consumption was especially evident in batch no. 5 where a greater loss of data occurred. A major system breakdown strongly affected data recordings as it ap-pears from the plot of ‘water/feed’ ratio in figure 3.6.

bat ch=5 pen=4

W/ F

wf

2

3

4

5

6

day

0 10 20 30 40 50 60 70 80 90 100

Figure 3.6 An example of recordings of the “water/feed’ ratio from batch no. 5 (pen no.4).

Although the registrations from the Cook’s influence statistics did not reveal serious problems with data from batch no. 5 it was decided to exclude them from the analyses, because of the loss of data for that period. Such a major lack of data could violate aims of finding any curvature in the general pattern. Diagrams in figure 3.7 show some irregularity also in data from batch no. 2. The diagram in figure 3.7A shows the development of the ‘water/feed’ ratio observed from pen nos. 5, 7 and 8. According to the logbook pen no. 6 contained invalid water data, so this data series was removed from the analyses.

Bat ch no. 2

pen 5 7 8

1

2

3

4

5

6

day

20 30 40 50 60 70 80 90

bat ch=2 pen=5

W/ FWat erFeed

0

1

2

3

4

5

6

7

8

9

10

11

12

13

day

0 10 20 30 40 50 60 70 80 90 100

Figure 3.7A: Development in the ‘water/Feed ratio’ during the growth period of pigs belonging to batch no. 2 , pen no. 5, 7 and 8. B: The development in the daily water and feed per pig and ‘water/feed’ ratio for pen no. 7.

There was a lack in data recordings of water consumption from batch no. 2 for a longer period (approx. between day 55 and day 74). As shown in figure 3.7B it is obvious that a rapid drop in the water level caused the change observed on the ‘water/feed’ ratio. The inconsistency in water data


was probably caused by an error in the water monitoring system as all pens showed an identical change in pattern. This was also supported by the fact that no other registrations in the logbook could explain any sudden change in the level of water consumption. Therefore the change in pattern was dealt with in the modelling procedure by introducing a fixed effect or a dummy variable as ex-pressed by Weisberg (1985). Medical conditions and vaccinations found influencing raw data were also excluded from the data set before further analyses of data were performed. Table 3.3 summarises the number of days where data regarding the ‘water/feed’ ratio have been excluded according to stated reasons. Invalid water registrations have seriously affected data quality in this study, as also previously described. Table 3.3 Summarising invalid data according to ‘water/feed’ ratio (days within all time series) (Exclusion of data from batch no. 5 is not included in the table). Batch no. 1 2 3 5 4 6 Total Habitation period 56 48 48 n/a 32 48 232 Invalid water registrations 40 2241 93 n/a 42 1381 537 Medical condition (treated) 14 - - n/a - - 14 Vaccinations 2 41 15 n/a - 16 65 Pigs removal 1 3 1 n/a 5 3 13 Unidentified problem - 8 9 n/a 1 - 17 1) Complete time series have been excluded. Figure 3.8 shows the average levels of the ‘water/feed’ ratio after the validation process and as we can see there remained some difference between average levels observed.

0

12

3

45

6

0 1 2 3 4 5 6

Batch no.

'wat

er/fe

ed' r

atio

W/F mean

Max.

Min.

0

12

3

45

6

0 1 2 3 4 5 6 7 8 9

Pen no.

'wat

er/fe

ed' r

atio

W/F mean

Max.

Min.

Figure 3.8A and B Mean levels of “Water/feed’ ratio between batches and between pens after data validation.

After data validation was performed the correlation between daily levels of water and feed intake were 0.80 on average.

3.2.2 Time interval appropriate for studying ‘water/feed’ ratio As stated in the introduction part of this study a central aim was to determine an appropriate interval for studying ‘water/feed’ ratio in growing pigs, and as described in section 3.1 conditions between


groups of pigs (pens) were very similar. Therefore further attention is paid towards diurnal patterns in this subsection, however the results supported the ones found in literature. A graphical examination of the diurnal pattern of feed and water consumption revealed strong fluc-tuations, making it difficult to analyse data on a shorter time step horizon (1 to 6 hours). A simple examination of the recordings of feed intake revealed a high occupation rate of the feeder with 14 pigs in each pen. The single space feeders appeared to be occupied approximately 80% of the time in the time interval from 0600 until 2000 H, at the same time as the accessibility to water for the individual pig was considered to be much less constrained because of a higher consuming rate. A high occupation rate of the feeders was most pronounced at the beginning of the growth period with a small decline, as the pigs got older, which could indicate that pigs have some behavioural change in their feeding pattern as they get older. This finding was also in line with the general development in eating patterns reported in chapter 2. The graphs in figure 3.9 and 3.10 illustrate a typical pattern observed in the development of the ‘water/feed’ ratio on a 1-hour and a 3-hour basis respectively (batch no. 3, pen no. 2, day 69 – day 78). Both graphs show strongly fluctuating patterns over a relatively short time period (not strictly diurnal), and several hours with water consumption only, yielded high ‘water/feed’ ratios.

0

10

20

30

40

50

60

70

29-jul 30-jul 31-jul 01-aug 02-aug 03-aug 04-aug 05-aug 06-aug 07-aug

'Wat

er/F

eed'

ratio

(l/k

g)

'Water/feed' - 1 hour

Figure 3.9 ‘Water/ Feed’ ratio on a 1-hour basis for a 10 day period (batch no. 3, pen no. 2).

0

1

2

3

4

5

6

7

8


'Wat

er/F

eed'

ratio

(l/k

g)

'Water/Feed' - 3 hours

Figure 3.10 ‘Water/ Feed’ ratio on a 3-hour basis for a 10 day period (batch no. 3, pen no. 2).

Figure 3.11 show the ‘water/feed’ ratio also observed on a 3-hour time step horizon from the neighbouring pen (no.3) within the same time period. There is not apparent similarity between pat-terns of the ‘water/feed’ ratio from the two pens.


0123456789

10


'Wat

er/F

eed'

ratio

(l/k

g)

'Water/Feed' - 3 hours

Figure 3.11 ‘Water/ Feed’ ratio on a 3-hour basis for a 10 day period (batch no. 3 pen no. 3).

As diurnal patterns of the ‘water/feed’ ratio did not show a similar stability in figures, as Madsen (2001) has found in separate analysis of water consumption, it was decided to focus on daily levels in the further data analysis of this study. Plots on 6 and 12-hour basis did similarly not provided consistent patterns on a day-to-day basis or between pens. The choice of 24 hour intervals was also supported by the general findings in literature (chapter 2), as diurnal patterns of water and feed con-sumption appear to be highly susceptible to local conditions like influence of social constraints, climatic conditions, etc. The diagram in figure 3.12 illustrates the ‘water/feed’ pattern observed on a daily basis for the same time series as shown in figure 3.9 and 3.10 (batch no. 3, pen no. 3, day 69 – day 78). This graph shows a relatively constant ‘water/feed’ ratio on day-to-day basis for the same time period.

0

1

2

3

4

5


'Wat

er/F

eed'

ratio

(l/k

g)

'Water/Feed' - day

Figure 3.12 ‘Water/ Feed’ ratio on a daily basis for a 10 day period (batch no. 3, pen no. 2).

Taking a quick look at figure 3.4 on page 37 showing data for a longer period of time reveals that a longer time step than 24-hours could possibly be relevant. A disadvantage of using longer intervals in the analyses would be that an invalid recording would yield a larger loss of data. Another way of analysing data with reduction of variance could be to use the method of ‘moving average’. A disad-vantage of this method is a lack in the general assumption of independency between observations.

3.2.3 Statistical methods As shown in chapter 2 variations in water and feed consumption could be related to factors like cli-matic or physical conditions, difference in breed and possible interactions between the factors. Therefore it was important that methods, applied to analyse and interpret the ‘water/feed’ ratio, was consistent with general biological principles in order to accommodate for apparent variation during


the growth period of the pigs. A central aim of analysing the pattern was to gain information about consistency during the growth period of the pigs. It was also desirable to draw inferences about pos-sible effects of factors that could cause variation between different groups of pigs. Finally it was desirable to examine whether variation in the ‘water/feed’ ratio was primarily a response to fluctua-tions in water or feed intake. ‘Water/feed’ ratio versus water and feed consumption The ‘water/feed’ ratio is derived from two individual recordings, water and feed consumption re-spectively. Awareness was needed, when analysing the ‘water/feed’ ratio, that the water recordings and the feed recordings must both be accurate, since an error in either of these affects the ratio. This also supports the relevancy of examining the sequence of water and feed consumption individually to see whether variation in the ‘water/feed’ ratio mainly originates from water or feed consumption curves. Basic effects - fixed and random When establishing the statistical models it was necessary to consider the nature of factors expected to affect water and feed consumption as well as the measurements made in the field data available. Whether factors could be contributing to a fixed or a random variation were considered. According to results from the literature review in chapter 2, factors of relevance from the data available in this study were pen, batch, breed and live weight at insertion into the building. The live weight at inser-tion was the average LW within each pen. The factors considered was primarily the ones that were expected to affect daily levels of water and feed intake rather than those only affecting diurnal pat-terns. The water meters used for recording the water consumption have primarily been designed for detec-tion of deviations in the diurnal drinking patterns rather than measurement of absolute levels. Under usual conditions the gages would also be used on larger groups of pigs than on a single pen. There-fore some systematic variation in the ‘water/feed’ ratio between pens could be expected, however the accuracy of the type used was higher than normal (see section 3.1.2). Although every pen in the-ory was physically identical, some systematic variation could also be expected between pens, as some pens were closer to the door or end wall etc. Considering these factors the individual ‘pen ef-fect’ was chosen as a fixed effect in the statistical analysis. Unfortunately in this study, animals of specific breeds were nearly always placed in the same pens, thus confounding the analysis of factors influencing the results; i.e. is a possible difference in ‘water/feed’ ratio noted due to animal breed or a possible consequence of being in a particular pen? Therefore did possible differences between breeds add an extra dimension to the fixed ‘pen effect’.


Live weight at insertion into the building was considered as a fixed covariate. Average LW at inser-tion was 24.75 kg (s.d. 1.86 kg). As described in chapter 2, climatic conditions and, in particular temperature, play an important role in daily water and feed intake in growing pigs, especially in situations with extreme higher (or lower) temperatures. Unfortunately registrations of either outdoor or indoor temperatures were not made. However, it was apparent that variation between observations from different batches of pigs could be caused by a seasonal (climatic) variation. Because the data set did not contain sufficient repetitions over the seasons of the year, and because the batch periods were not identical (same time of the year) the effect of ‘batch’ was considered to be random. A dummy variable was chosen as a fixed effect to describe the unexplained level change in water intake recordings and ‘water/feed’ ratio in time series from batch no. 2 as described in section 3.2.1. Day of observation was considered to be a covariate, and a more advanced theory with models of repeated measurements and coefficients of random regression were applied. Model Choice A description of the development in water and feed intake and ‘water/feed’ ratio as a function of time (age of the pigs) was desired. Each combination of batch and pen representing a single time series was defined as an experimental unit. To separate within- and between-group (of pigs) varia-tion, a polynomial model with coefficients of random regression was found to be appropriate. This was necessary to obtain parameter estimates for average curves and to accommodate for group de-viation from the average curves. Random regression models, of which the models used are exam-ples, is similar to the class of models (mixed models), which are commonly used in animal breeding (Meyer, 1998). The model below shows the chosen starting model for analysing patterns of water and feed con-sumption separately, along with the combined ratio. Factors and covariates in the models were as previously described.


Starting models: Yijkl = (β0 + B0ij) + Ai + γj + αWij+ δk(i,j.l) + (β1 + B1ij)X1(tijl) + (β2 + B2ij)X2(tijl) + β3X3(tijl) + β4X4(tijl) + eijl + εijl where: Yijlk Response values of either: water, feed or ‘water/feed’ ratio

i = batch no.1, 2, 3, 4, 6 j = pen no.1, 2, …, 8 k = 0,1 l = day no. l ,2,…., approx. 95 (after insertion in into the building) Ai ~ N(0,σ2

A), random effect of ith batch, independent of each other γj fixed effect of pen α regression parameter (related to live weight at insertion into the building) δk(i,j,l) fixed effect (dummy variable to explain change in water level (batch no. 2) β0 overall intercept B0ij ~ ( )2

0,0 BN σ , independent of each other (random intercept)

β1 regression parameter B1ij ~ ( )2

1,0 BN σ , independent of each other (random regression parameter)



β3 regression parameter β4 regression parameter Wij average live weight at insertion into the building within each time series X1(tijl) 1st orthogonal polynomial according to time of observation i,j,l X2(tijl) 2nd orthogonal polynomial according to squared time of observation i,j,l X3(tijl) (time of observation i,j,l - 49)3 (centered data) X4(tijl) (time of observation i,j,l - 49)4 (centered data) eijl ρeijl-1 + uijl, where uijkl ~ N(0, σ2

u) and independent ρ correlation parameter for the first order autoregressive process εijl ~ N(0,σ2), independent of each other – (included by using the local option in SAS) ti.l = 0 is the time where the first group enters the building.

NB: δk(I,j,l) was not considered in the analysis of the feed consumption, as the disturbance described in section 3.2.1 only affected recordings of the water monitoring system. Consequently this parameter was only relevant for the analyses of water intake and ‘water/feed’ ratio.

To obtain the criteria of independency between regression coefficients of random effects, it was necessary to use co-variance functions described by orthogonal polynomials. The two orthogonal polynomials of interest in this study were estimated as: X1(tijl) = tijl-49 and X2(tijl) = (tijl-49)2-851 See appendix 4 for further detail about estimation of the orthogonal polynomials. Considering the coefficients of random regression a structured co-variance was assumed, to enable easy processing by the statistical software. The co-variance structure for the random regression co-efficients B0, B1 and B2 are assumed independent:


=

2

2

2

2

1

0

2

1

0

000000

B

B

B

ij

ij

ij

BBB

Varσ

σσ

In SAS the structured correlation structure is denoted by type=VC. Repeated measurements of water and feed intake were recorded within each group of pigs (experi-mental unit). An experimental unit was designated as an individual time series recorded on a pen level within each batch of pigs. Because of this design highly correlated measurements within time series were expected, and a first order autoregressive co-variance structure was chosen, as shown in the formula below.

et = ρet-1 + ut, for t>2 The parameter ρ is the regression parameter describing the autocorrelation, and ut are the innovation error usually assumed to be N(0,σ2

u).

where:

−

= 22

11)(ρ

σ uteVar (see appendix 5 for further detail).

In the process of choosing an appropriate error structure the spatial Gaussian type was also tried, however this method caused convergence problems and was not used. The first order autoregressive process was supplemented by a random observational error compo-nent εt. This meant that the residual variation was split into two parts, an auto correlated component et and an independent residual component εt. This was to accommodate for apparent measurement error not fitting into the assumed AR(1) process. 3.3 Results This section will focus on results of the data analysis of water and feed consumption and the com-bined ‘water/feed’ ratio. A test was completed to determine whether raw or transformed values should be considered. Model reductions were preformed using statistical tests to obtain the final models, which are capable of describing the 3 patterns (water intake, feed intake and ‘water/feed’ ratio. 3.3.1 Raw or transformed response values After the statistical models were established focus was then on whether raw or transformed values of the response variable should be considered. Residual plots were produced by an approximate


method described by Hox (2002) of plotting standardised residuals against predicted values using the fixed part of the models. A trial of logarithmic and other transformations (e.g. √X, 1/x) were compared in order to decide on which provided the most acceptable residual plots. Logarithmic transformations of the water and feed data appeared to yield the most satisfactory results, as funnel shapes in the residual plots were eliminated. The residual plots can be seen in appendix 6. Residual plots from raw and logarithmic transformed values of the combined ‘water/feed’ ratio yielded simi-lar results. Although the plots were of similar quality, logarithmic transformation of the ‘water/feed’ ratio was chosen to enable easier interpretation of the results between the different analyses. Easier interpretation were also enhanced because of the general rule of mathematics:

( ) ( )FeedLogWaterLogFeed

WaterLog −=

It was noted that the logarithmic transformed ‘water/feed’ ratio was found to be the same as the dif-ference between logarithmic transformed values of the two curves separately. 3.3.2 Statistical test and model reduction Statistical tests were performed using the ‘Proc Mixed’ procedure in the software packet SAS ver-sion 8.2. The method of restricted maximum likelihood (REML) is the default mode when using ‘Proc Mixed’, however, Maximum Likelihood (ML) was used in the statistical analyses of this study. Using SAS (Proc Mixed) solutions were found by iteration using the Newton-Raphson algo-rithms (SAS online Doc, 2003). The ML method was chosen to ensure easy comparison between different models, as this method is invariant to one-to-one reparameterisations of fixed effects (Pin-heiro and Bates, 2000). The starting models established were checked for possible model reductions with various methods depending on the actual step. Non-significant parameters were removed one by one (backwards elimination). Non-significant random effects were removed from the model by means of Aikeke’s information criterion (AIC). However appropriateness of the chosen two-component error structure (et + εt) was tested with a quotient test (G2). AIC is a measure of relative information in the tested model compared to a model with all possible terms included (Cook and Weisberg, 1999). There-fore, model reductions associated with lower AIC values were to be accepted. A quotient test (G2) was used to test whether the class of model were appropriate (model of re-peated measurements). In the quotient test G2 expresses the difference between –2 x LOG LIKELI-HOOD estimates for the two models:

G2 = 2 x (LOG LIKELIHOOD2 - LOG LIKELIHOOD1) ~ χ2(df2-df1)

(Index 1 denotes the simpler model)


Fixed effects (and regression coefficients) were tested with partial F-statistics. First removed pa-rameter resulted in the smallest decrease in R2, thus the smallest partial F-statistic (Myer, 1990). Brief results of statistical tests Table 1 to 3 in appendix 7 summarises the results of the statistical model reductions. Briefly de-scribed, curvature was found in all three analyses, although most surprising was the quadratic pat-tern found in the ‘water/feed’ ratio. In the analysis of feed consumption the random gradient (B1ij) and the fixed cubic regression coefficient (β3) showed significant effect, although the latter was es-timated to a value close to zero. Random gradients of the water analysis and ‘water/feed’ analysis were all non significant or esti-mated to a value of zero by SAS. Random intercept (B0ij) was found to be significant in the water and ’water/feed’ analyses as ex-pected, and this parameter was also significant in the analysis of feed consumption. Random batch (Ai) effect did (unexpectedly) not show significance in any of the analyses. Fixed effect of pens (γj), was found to improve model performance on the combined ‘water/feed’ ratio whereas the influence on analyses of water and feed separately were non-significant. Fixed effect of live weight at insertion into the building (α) affected feed intake, but not water in-take or ‘water/feed’ ratio.

Fixed effect of the dummy variable δk(i,j,l), responsible for an unexplained jump in water registra-tions, did show significance with regard to water levels and also the ‘water/feed’ ratio in batch no. 2 as expected. The two-component error (eijl+εijl) structure was found acceptable in all three models.


3.3.3 Final models According to the tests performed (appendix C, table 1-3), the analyses yielded final models as shown:

Water: Yijkl = (β0+B0ij) + δk(i,j.l) + β1 X1(tijl) + β2 X2(tijl) + eijkl + εijkl

Feed: Yijkl = (β0+B0ij) + αWij + δk(i,j.l) + (β1+B1ij)X1(tijl) + β2X2(tijl) + β3X3(tijl) + eijkl + εijkl

‘Water/feed’ ratio: Yijkl = (β0+B0ij) + γj + δk(i,j.l) + β1X1(tijl) + β2 X2(tijl) + eijkl + εijkl

where: Yijlk Response values of either: water, feed or ‘water/feed’ ratio

i = batch no.1, 2, 3, 4, 6 j = pen no.1, 2, …, 8 k = 0,1 l = day no. l ,2,…., approx. 95 (after insertion in into the building) γj fixed effect of pen α regression parameter (related to live weight at insertion into the building) δk(i,j,l) fixed effect (dummy variable to explain change in water level (batch no. 2) β0 overall intercept B0ij ~ ( )2

0,0 BN σ , independent of each other (random intercept)



β2 regression parameter β3 regression parameter Wij average live weight at insertion into the building within each time series X1(tijl) 1st orthogonal polynomial according to time of observation i,j,l X2(tijl) 2nd orthogonal polynomial according to squared time of observation i,j,l X3(tijl) (time of observation i,j,l - 49)3 (centered data) eijl ρeijl-1 + uijkl, where uijkl ~ N(0, σ2

u) and independent ρ correlation parameter for the first order autoregressive process εijl ~ N(0,σ2), independent of each other

As previously seen a double component error structure was chosen and found appropriate for the analyses of this study. Components of the variance co-variance matrix for the residual error (et+εt) can be expressed:

( ) ( )( ) ( )01

1, 22

2|| =+

−

=++ + nIeeCov un

nijklijkl εσρσρεε


If f1=e1 + ε1, ……, fn=en+ εn , then:

22

2

21

321

232

12

121

10....00001....000........00....10000...01000...001

1

1....1....

............1...1...1

.

.

.

.

εσρσ

ρρρρρρρρ

ρρρρρρρρρρρρ

+−

=

−−

−−−

−−

−−

−

u

nnn

nnn

nn

nn

nn

nf

f

Cov

=

++

++

+

−−

−−−

−−

−−

−

22222212

222232221

222322222

21222222

22122222

....

............

..........

ε

ε

ε

ε

ε

σσρσσρσρσρρσσσσρσρσρ

σρσρσσρσσρσρσρρσσσρσσρσρσρρσσσ

eeen

en

en

eeen

en

en

en

en

eee

en

en

eee

en

en

eee

Table 3.4 – 3.6 show random and fixed parameter estimates for the three final models. Table 3.4 Random parameter estimates

Water Feed ‘Water/feed’ Parameter Trait Estimate (s.e.) Estimate (s.e.) Estimate (s.e.)

σ2B0 Random int. 0.01058 (0.003139) 0.003671 (0.001007) 0.004980 (0.001816)

σ2B1 Random 1th

regressor - 1.859E-6 (~ 0) -

σ2u - 0.007754 (0.001341) 0.004497 (0.000622) 0.007221 (0.001076)

ρ - 0.9358 (0.01578) 0.7867 (0.06976) 0.9236 (0.01768) σ2

ε - 0.006203 (0.000253) 0.009078 (0.000613) 0.004734 (0.000229)

Table 3.5 Fixed effect parameter estimates Water Feed ‘Water/feed’ Parameter Trait

Estimate (s.e.) Estimate (s.e.) Estimate (s.e.) β0 Intercept 1.8044 (0.01914) 0.2761 (0.1400) 1.0727 (0.03749) β1 1th regressor 0.008923 (0.000299) 0.01015 (0.000457) -0.00197 (0.000279) β2 2nd regressor -0.00014 (0.000011) -0.00012 (8.438E-6) -0.00003 (0.000011) β3 3rd regressor - 7.505E-7 (~ 0) - α LW(start) - 0.01788 (0.005619) - γ1 Pen 1 - - 0.1220 (0.0562) γ2 Pen 2 - - 0.0280 (0.0529) γ3 Pen 3 - - -0.0208 (0.0562) γ4 Pen 4 - - 0.0135 (0.0535) γ5 Pen 5 - - 0.0538 (0.0529) γ6 Pen 6 - - -0.0986 (0.0559) γ7 Pen 7 - - -0.0596 (0.0529) γ8 Pen 8 - - 0 (-) δ0 - 0 (-) 0 (-) δ1 Dummy 0.1466 (0.03009) Not relevant 0.116 (0.0278) Table 3.6 Type 3 tests of fixed effects


Water Feed ’Water/feed’ Parameter Trait P-value P-value P-value

β1 1st regressor <0.0001 <0.0001 <0.0001 β2 2nd regressor <0.0001 <0.0001 0.0026 β3 3rd regressor 0.34NS 0.041 0.17NS α LW (start) 0.14NS 0.003 0.27NS γj Pen 0.13NS 0.12NS 0.021 δ1 Dummy <0.0001 - <0.0001

Figure 3.13 shows the mean predicted daily levels of water and feed intake per pig over time.

0

2

4

6

8

10

0 (25 kg)

20 (35 kg)

40 (55 kg)

60 (80 kg)

80 (95 kg)

95 (98 kg)

Days after insertion (approx. LW, kg)

Water (litre)Feed (kg)

Figure 3.13 Mean predicted values of water and feed intake in growing pigs according to time in days after insertion at approximately 25 kg live weight. Notice: the LW’s shown in brackets are only approximate average figures.

It is obvious that the growing pigs increased their daily levels of water and feed intake with increas-ing age (and body weight). The declining rate of increase in water and feed intake at the end of the observation period as shown in figure 3.13 is a response of the fastest growing (heaviest) pigs leav-ing the pens as they reached LW for slaughter and a tendency of declining ‘water/feed’ ratio accord-ing to age. Average ‘water/feed’ ratio decreased from approximately 3.1 to 2.6 (untransformed val-ues) as can be seen in figure 3.14.

0

1

2

3

4

0 (25 kg)

20 (35 kg)

40 (55 kg)

60 (80 kg)

80 (95 kg)

95 (98 kg)

Days after insertion (approx. LW, kg)

litre

/kg Water/feed' ratio

LowerUpper

Figure 3.14 Average ‘water/feed’ ratios according to time after insertion into the building at approximately 25 kg live weight. Notice: this graphs is based on fixed effects of the final model, however pen was considered as a random effect (rather than fixed). Confidence limits were derived from standard errors derived of fixed effects parameters only. The statistical tests performed showed that a linear decrease was not sufficient to describe the de-clining ‘water/feed’ ratio over time. A maximum level of the polynomial function appeared 16 days


after insertion into the building, although this estimated point of maximum did not play a crucial role. The parameter estimates obtained from the statistical analysis will be discussed in chapter 4; firstly a further investigation of the model fit to the data analysed is required. 3.3.4 Model check A central part in these analyses has been the choice of a statistical model with an appropriate co-variance structure capable of describing the pattern in the data analysed. A first order autoregressive (exponential correlation) model was applied in all three processes. The two diagrams in figure 3.15 show the pattern of the lagged residual values as a function of the actual residual values from the ‘water/feed’ ratio (batch no. 3). The plot of the single lagged residuals shows (as expected) a stronger autocorrelation than the plot of the residual values lagged by four time steps. This indicates that the correlation between measurements decreased as the time separation between measurements was increased.

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According to the quotient tests performed, the first order autoregressive AR(1) error structure was not sufficient to fit data, and the two component error (et+εt) structure was appropriate. As it ap-pears from figures in table 3.4 correlation for et were quite high as ρ varied from approx. 0.79 to 0.94. It also appears that the lower ρ was; the more weight was on εt in proportion to et. The feed curve analyses had the lowest ρ, but at the same time this analysis also yielded a significant 1th or-der random regressor (B1). Based on quotient tests it was concluded that the two-component error structure (et+εt) was an acceptable choice in all three models. It is possible that an extension of the model to a higher order autoregressive process might have lead to a better fit of the model. Unfortu-nately the SAS procedure ‘Proc Mixed’ is not capable of handling higher orders of autoregressive processes. As the fit of an AR(1) process combined with a random residual error was considered to be acceptable, this topic was not further analysed.


Residual plots The diagrams presented in figure 3.16 (and figure 3.17) illustrate examples of approximate stan-dardised residual plots as decribed by Hox (2002). All plots in figure 3.16 are based on recordings from the same time series (Batch no. 4, pen no. 6). Graphs on the left show standardized residuals plotted against time, whereas graphs on the right show standardized residuals plotted against the predicted values based on fixed effects.


Figure 3.16 Std. residual plots for batch no. 4 pen no. 6. Left graphs: std. residual values plotted against time. Right graphs: std. residual values plotted against the predicted value based on fixed effects.

The diagrams in figure 3.16 show a general fit of the models to the data. However certain time se-ries’ did show larger deviations from the expected pattern. Examples of extreme deviating cases from each of the three analyses are shown in figure 3.17.

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Figure 3.17 Std. residual values plotted against the predicted values based on fixed effects. Plots are based on 3 ex-treme deviating time series.

The inconsistent pattern of residual plots observed in certain time series’ clearly indicated that ran-dom effects and the residual error play an important role in model performance. This was although a random gradient were only significant in the feed analysis.

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3.3.5 Model performance Model performance plots of the logarithmic transformed response values are presented in the same diagrams as the predicted values with their corresponding upper and lower confidence limits. Such diagrams are presented in figure 3.18, based on results from batch no. 2, pen no. 2 and results from batch no. 6, pen no. 7.

Figure 3.18 Observed logarithmic transformed response values of water, feed and ‘water/feed’ ratio along with pre-dicted values shown with their corresponding confidence limits. Left diagrams: results from batch no. 2, pen no. 2. Right diagrams: results from batch no. 6, pen no. 7.

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In the analysis of data from batch no. 2 a dummy variable was introduced to describe variation caused by an unexplained jump in the general level of the water recordings after a failure in the wa-ter monitoring system. This change in pattern also appears in the graphs on the left of figure 3.18 which describes water-associated patterns from batch no. 2, pen no. 2.

Figure 3.19 and 3.20 shows how observed values of ‘water/feed’ ratio vary around the mean pre-dicted values within pen no. 5 and pen no. 8. The observed values represent all batches (except batch no. 5).

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Figure 3.21 shows how observed values of water and feed consumption per pig vary around the mean predicted values. The observed values represent all batches (except batch no. 5).


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It is obvious from the two graphs in figure 3.21 that curves of water intake is associated with most random variation around the mean predicted levels, which also is obvious according to the random parameter estimates in table 3.4. Therefore the majority of random variation in ‘water/feed’ origi-nates from the water curves, although the model describing feed consumption comprised most ran-dom parameters. As response values have been logarithmic transformed, it follows that approximate coefficients of variation easily can be determined (Stryhn et al., 1997).

( ) ( ) ( )XCVEX

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Approximate coefficients of variation according to the random intercepts are shown in table 3.7. Table 3.7 Approximate coefficients variation according to random intercepts. Random intercept Water Feed ‘Water/feed’ ratio Approximate coefficient of variation 10% 6%1 7%2 (9%)3 1) Model describing feed intake comprised a 1st order random coefficient, however the value was low. 2) Model describing ‘water/feed’ ratio comprised fixed ‘pen’ pen effects. 3) Model describing ‘water/feed’ ratio without a fixed ‘pen’ effect

If the fixed ‘pen’ effect in the model behind ‘water/feed’ ratio was excluded, then the approximate coefficient of variation was increased to 9%, which would enable a better comparison between models. Figure 3.22 shows that time series with high values of the feed consumption were also as-sociated with high values of water consumption, as a correlation of 0.50 between figures existed. In this graph values of random intercept from time series’ of water data have been plotted against val-ues of random intercept from time series’ of feed data.


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To examine whether residual values from analyses of water and feed consumption curves also were associated with some sort of correlation, diagrams were constructed as shown in figure 3.23 and 3.24. The raw residual values were created by means of the option ‘outp’ in SAS ‘Proc Mixed’. Correlation between the residual values from water and feed analyses was found to be 0.51 on aver-age.

Figure 3.23 General examples of residual values obtained from water analysis according to residual values obtained from feed analysis from specific time series.

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Plots in figure 3.23 show general patterns of the residual values plotted against each other, whereas plots in figure 3.24 reveal certain time series with a poor correlation.

Figure 3.24 Residual values obtained from water analysis according to residual values obtained from feed analysis from specific time series with a low correlation in figures.

3.4 Chapter summary ‘Water/feed’ ratio and consumption patterns of feed and water from approx. 670 pigs has been ana-lysed during the course of this chapter. Preliminary data analysis indicated that 24-hour time scales were appropriate in order to analyse the time patterns. Although the field data was associated with some problems regarding the water intake recordings it was possible to estimate mean curves and parameter estimates for variation between time series’. In this process random regression models with a first order autoregressive error structure were used. The overall results showed that the mean curve for ‘water/feed’ ratio was characterised by a declining pattern over time, as shown in figure 3.14, page 50. The more detailed results of this chapter and performance of the analyses are dis-cussed in chapter 4.

Batch no. 4, pen no. 7 Batch no. 6, pen no. 8

Chapter 4 Discussion ________________________________________________________________________________

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4 Discussion This chapter will focus on patterns of ‘water/feed’ ratio in slaughter pigs, and the influences of physiological, social and environmental factors. These influences will be discussed with regard to different time intervals, and conclusions regarding measurements over 24 hour periods will be made. Finally, discussion of odd incidences affecting the ‘water/feed’ ratio will occur, along with a discussion of the limitations of this study. In section 4.1 final conclusions obtained fro this study are presented. Diurnal patterns of water and feed intake generally have one or two daily peaks in level (i.e. Hyun et al., 1997; Young and Lawrence, 1994; Madsen, 2001) (section 2.2.1). This daily stability in con-sumption suggested that diurnal patterns of ‘water/feed’ ratio would show a similar consistency. Therefore attention to underlying factors of the ‘water/feed’ ratio was required to elucidate whether consistent patterns of the ratio in groups of pigs could be expected within shorter or longer time intervals. As described in chapter 2, drinking patterns and feeding behaviour are influenced by the state of the animals and by environmental factors (e.g. Bigelow and Houpt, 1988; Haer and Vries, 1993; Petherick et al., 1989; Turner et al, 2000; Young and Lawrence, 1994). State of the animal is defined as age, sex, breed and nutritional and physiological status. Behavioural changes according to the age of the pigs appears to follow a general time pattern and time (age) is an easy parameter to measure, which infers that such influences could be considered for analytical purposes. Changes in diurnal feeding (and drinking) behaviour related to animal age have not been investigated inten-sively in the data analysis of this study. But we know from the literature that as the pigs’ get older total daily feeding time and meal frequency decline while total intake increases according to a higher consumption rate (e.g. Hyun et al., 1997; Morgan et al., 2000; Liang and Wood-Gush, 1984; Labroe et al., 1994; Bigelow and Houpt, 1988). The preliminary data analysis of this study indi-cated a decline in the occupation rate of feeders, which corresponded to results from literature (Hyun et al., 1997; Labroue et al., 1991; Morgan et al, 2000; Nielsen et al, 1995). An aim of this study was to determine an appropriate time interval for the accumulation of data in order to find consistent time patterns of ‘water/feed’ ratio in groups of pigs. In addition to the state of the animals, social and environmental factors also impact on feeding and drinking patterns. Some of the relevant factors affected water and/or feed intake temporarily whilst others have a more long-term impact. Therefore in the analysis of ‘water/feed’ ratio it was relevant to distinguish whether daily levels or only diurnal patterns are affected by the certain conditions. As described in the pre-vious chapters, there are several indications that diurnal patterns of ‘water/feed’ ratio in groups of pigs is highly variable due to several short-term impacts affecting water and feed intake. As a result it is concluded that ‘water/feed’ ratio in groups of slaughter pigs should only be considered within intervals not shorter than day length. The appropriateness of using 24-hour time frames was con-firmed by the preliminary data analysis of this study where almost identical pen conditions were


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expected. Even under these homogenous and strictly controlled pen conditions consistent diurnal patterns of the ‘water/feed’ ratio were not present. It would be difficult to consider impacts on the ‘water/feed’ ratio according to differences in sex, particularly if groups were mixed. Literature shows that castrated males have a higher daily total feed consumption because of a higher meal frequency than boars or sows (Cole and Haresign, 1985; Labroe et al., 1994) however, contrasting results were found by different authors (Hyun et al., 1997). There are also indications that female slaughter pigs may come in to oestrus prior to slaugh-ter (Thorup, 2003). Consequently this could cause fluctuating patterns of ‘water/feed’ ratio as pigs in oestrus are expected to decrease their daily feed intake (Whittemore, 2000). The findings from literature suggested that groups of pigs should be of the same ‘sex’ within groups. Thus, impacts of specific sexes on the ratio would need special attention according to daily measurements of ‘wa-ter/feed’ ratio between groups of pigs. The pigs participating in the data analysis of this study (chapter 3) were all boars, so results according to sex differences was not obtained. From the literature it appears that different breeds can have variations in diurnal feeding behaviour, however considerable differences in total daily feed intake has not been reported. Under practical conditions ‘breed’ differences would also be less relevant, as most pigs on commercial farms are mixed breeds of a specific type. As mentioned in section 3.1.1 all animals participating in the data analysis of this study were pure breed animals. Specific breeds were nearly always placed in the same pens, thus confounding the analysis of different factors. The general allocation of specific breeds was shown in figure 3.2 (section 3.1.2). According to the literature impacts on daily feed intake of different breeds are marginal and generally pigs are of similar breed within herds. There-fore this factor need not be considered, although it did play a role in the data analysis of this study. Environmental factors of the pigs were found to have a significant influence on levels and patterns of water and feed consumption within shorter or longer time intervals. As seen in chapter 2 some factors are of more primary character than others. Table 2.7 (section 2.7) shows factors of rele-vance, which include environmental conditions (e.g. ambient temperature, provision of light) and social factors (i.e. competition levels). Other factors explored were impacts of human activity and composition of feeds offered to the animals (not in table 2.7). Examples of secondary factors are housing conditions or group size according to feeder or drinker allocation, which can influence competition levels. All these factors can have an impact on changing diurnal patterns, however some of them have longer-term impacts, which also affects daily levels of water and feed intake. Competition levels can cause diurnal variations in feed and water intake patterns, whereas total daily intakes and life performances (growth rate, feed conversion efficiency) are less affected, since pigs kept under restricted conditions will adjust their diurnal behavioural patterns (Ingram et al.,


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1980; Nielsen et al., 1995; Walker et al., 1991). Accordingly, if competition levels are not extraor-dinary high then daily levels of feed and water consumption should not be affected; e.g. <20 pigs per eating space (Nielsen et al., 1995), however various thresholds were reported by different au-thors. In the preliminary data analysis of this study diurnal feeding behaviour of pigs also appeared to be influenced by a constraint in relation to feeder access (one single space feeder to 14 pigs). It was noted that the type of feeding station used in this study (section 3.1.2), provided a high degree of protection while a pig was eating, thus causing increased competition levels as reported by Niel-sen et al. (1996) (section 2.5.1). Therefore, changes in diurnal feeding behaviour could be expected especially at peak hours of intake. Differences in competition levels between pens would especially be evident between groups, where some pigs were removed because they reached live weight ready for slaughter. Short-term impacts caused by different group sizes would therefore support that only daily levels of the ‘water/feed’ ratios between groups of pigs should be compared to obtain consis-tent patterns. Feed and water intake are dynamic responses, which can be influenced by thermal environmental conditions and exposure to different lighting regimes. Light patterns are strongly influencing diur-nal patterns of water and feed intake (Ingram et al., 1980). It appears from studies, which have ana-lysed combinations of temperatures and light regimes, that concurrent high temperatures over-whelm the effect of lighting, thus disrupting normal feeding rhythm. Generally changed light condi-tions only affect diurnal patterns of water and feed intake, whereas exposure to extreme tempera-tures (higher or lower) can cause severe pattern changes of total daily water and feed intake (Liang and Wood-Gush, 1984; Ingram et al., 1980; Feddes et al., 1989). Temperatures deviating strongly from the pigs’ comfort temperature are expected to influence patterns and levels of water and feed consumption. Lighting regimes mainly affect diurnal patterns, whereas the total levels of daily wa-ter and feed consumption are less affected. Inherent problems of the ambient temperature not been recorded in the data material analysed in this study are discussed further later in this chapter. To summarise, extreme temperatures are likely to affect daily levels of water and feed consumption, whereas influence of light plays a less important role. In the data analysis of this study water and feed intake per pig were analysed along with the com-bined ratio on a daily basis. In order to stabilise variance and to obtain acceptable residual plots response values of water and feed intake and ‘water/feed’ ratio were logarithmically transformed. The feed consumption was best described with a 3rd order polynomial regression function contain-ing random coefficients of 0th and 1st order. In contrast the daily water consumption was described with a simpler function and with more random variance (table 3.4). This was partly due to the inac-curacies of the water data gained, however day-to-day variation within groups of pigs also was also present. It was a problem that greater loss of water data occurred (see section 3.2.1). Logarithmic transformed values of the daily ‘water/feed’ ratio were described with a 2nd order polynomial func-


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tion (fixed part of the model), although random variation between consumption curves from differ-ent groups of pigs was observed. Impacts of these random and other fixed effects are discussed later in this chapter. Average figures of the ‘water/feed’ ratios decreased from approximately 3.1 to 2.6 (untransformed values) as can be seen in figure 3.14 (section 3.3.3). The statistical tests performed showed that a linear decrease was not sufficient to describe the declining ‘water/feed’ ratio over time. The overall results could indicate that the ‘water/feed’ ratio was relatively constant for the first 35 days after insertion into the building (until approx. 50 kg LW) before then declining gradu-ally. A decrease in the ‘water/feed’ ratio while live weight is increasing is similar to the pattern de-scribed by Pieterse (1963) where pigs were fed restrictively. Such a distinct declining pattern has not been identified in any of the more recent literature cited. It is concluded that a general decrease in mean ratios according to age existed, however the reasons for this were not quite clear. From the results obtained, it could be argued that pigs with a high growth rate reaching body weight for slaughter early might require higher intakes of water in rela-tion to feed. Thus remaining pigs at the end of the time series dominated patterns of ‘water/feed’ ratio in a decreasing manner. The declining water intake at the end of the time series (figure 3.13) would also support such an argument. It is obvious from the graphs (appendix 2) showing individ-ual time series of ‘water/feed’ ratio that fluctuations in daily patterns were more pronounced as group sizes decreased by the end of the observation period. Because of the strict data validation performed this impact was considered to be partly eliminated. The fact that the mean ratio may have changed because some pigs were removed may or may not be significant. However under tradi-tional farming conditions this pattern would always be evident as pigs are removed for slaughter gradually, as compared by an all in - all out production system. In all in–all out production systems pigs are generally delivered for slaughter within a period of 2-4 weeks (Danish conditions). As the ‘water/feed’ ratio is derived from water and feed intake, apparent variation in either of these two, contribute to variation of the combined ratio. Bigelow and Houpt (1988) reported that the mean level of the ‘water/feed’ ratio for a single pig was 2.14 with s.d. 0.46 over a 30-day period (figure 2.2, section 2.2). According to Bigelow and Houpt (1988) this day-to-day variation was primarily a consequence of daily variations in water intake rather than feed intake. It was obvious from the results of the data analysis in this study that recordings of daily feed consumption showed a higher stability in figures (lower residual variance) than did the recordings of daily water intake (section 3.3). The general results suggested that day-to-day variations of the ‘water/feed’ ratio could partly be eliminated by increased group sizes, as larger fluctuations of the ratio was recognised at the end of time series’ since some pigs were removed for slaughter. In this study with groups of 14 pigs the standard deviation of raw values for the ‘water/feed’ ratio was approx. 0.25 within most time series (assuming a constant level day 10-40). This figure was somewhat lower than the 0.46 reported by Bigelow and Houpt (1988), however it was also noted that the mean ratio was higher in


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this study. The variation in raw data around the (model) predicted mean levels is shown in figure 3.18-3.20 (section 3.3.5). Under most practical conditions water consumption would also be meas-ured on larger groups of pigs (e.g. house sections), which could possibly decrease the variation fur-ther. The result from the data analyses also showed that variation in water data was higher than in the feed data. Figure 3.21 (section 3.3.5) shows the distribution of the recorded raw values of water and feed intake around the mean predicted curves. The approximate coefficient of variation regard-ing the random intercept was 9% for the combined ratio implying the fixed ‘pen’ effect being ex-cluded from the model, however the corresponding figures were 10% for the water data and 6% for the feed data (table 3.7). The relative variation of ‘water/feed’ ratio between time series’ suggests that larger groups of pigs should be included in specific measurements. It is believed that this would make more reliable results of specific measurements at given time of observation. Average levels of ‘water/feed’ ratio in this study were similar to other results from literature (table 4.1), although variation between studies appeared.

Table 4.1 Average ‘water/feed’ ratio found in various studies. Author Approx. average

‘water/feed’ ratio This study 3.0 Bigelow and Houpt, 1988 2.0 Collin et al., 2001 3.0 Petersen, 1995 3.2 Pieterse, 1963 2.8 Smidth, 1990 3.0 Walker, 1991 1.8

As shown in chapter 2 such differences in average ‘water/feed’ ratio could be caused by differences in feed composition (McDonald et al., 1995) or housing conditions related to feeder or drinker de-signs (Petersen, 1995; Smidth, 1990). This supports the idea that a consistent relationship between water and feed intake over time exist, however, the exact levels depend on specific conditions. Therefore identical conditions between groups of pigs must be present and/or detailed knowledge about impacts of production systems, feed composition, climate, etc. must be known. In this study the general performance plots and the plots of residual misspecification in section 3.3 revealed that the fit of the three models caused some problems particularly in some time series’. The overall results showed that variation between groups of pigs existed. The random regression models partly accommodated such problems, however the general patterns of the data material were not sufficiently consistent to accommodate more advanced model specification. It was interesting to note the tendency shown in figure 3.22 (section 3.3.5) where high random in-tercept values regarding feed consumption were also characterised by a similar high value in ran-


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dom intercept for the water intake. The correlation between random intercept values was 0.50. In relation to the central point of this study (consistency of ‘water/feed’ ratio patterns), these results indicated that random variation associated with levels of water and feed consumption was generally correlated between models. Residual variation within time series showed a similar correlation be-tween analyses of water and feed intake. Examples of such patterns can be found in figure 3.23 (section 3.3.5). Although the average correlation was 0.51, the pattern was not distinct in all time series (figure 3.24). The random regression function describing feed consumption had a random gradient of 1st order, whereas such gradient did not appear in the analysis of the water data. The random gradient in the feed analysis could indicate that different breeds would have a different in-take curve, however this was not clear from the analysis performed (or literature reviewed). Whether a random gradient in the water analysis did not exist, or was due to poor data quality is not clear, but it is obvious that the time series of water intake is associated with significant random (and residual) variation. An obvious reason for the lack of model performance in some data series could be a shortage of relevant parameters in the models. A lack of important parameters is one of the disadvantages of using field data rather than proper trial data set up for a specific purpose. An example of a missing parameter is ambient temperature (e.g. average daily temperature or maximum daily temperature) and, therefore the results must be considered with this awareness. According to the literature, situa-tions with extreme ambient temperatures were the most likely to cause severe pattern changes in feed and water consumption, whereas smaller variations within pigs’ comfort temperature zones do not have a serious impact (e.g. Collin et al., 2001;Mount et al., 1971; Feddes et al., 1988; Nienaber et al., 1990). Whittemore (2000) stated that growing pigs’ comfort temperature decrease from 20ºC to 16ºC as body weight increases from approximately 25 kg to 100 kg, however the specific re-quirements depend on provision of bedding material, insulation of the building, etc. Further atten-tion to the ambient temperature is also paid in the next paragraph. Random intercepts was found necessary in the analysis of ‘water/feed’ ratio and in the analyses of water and feed consumption separately. These indicated differences in levels independent of ‘pen’ and ‘batch’ effects. The latter was not statistically significant in either of the analyses. Although ambient temperature was not recorded in this study it is possible that some variation in water and feed intake could be associated with time of the year differences. Therefore, variation between batches could have been expected due to seasonal variations even though batch periods were not fully in alignment with seasons of the year (e.g. batches corresponded to summer, winter periods, etc). As the climate at the experimental house was strictly controlled by means of central heating and ventilation, it is considered that temperatures under lower critical temperatures (LCT) did not occur, whereas extreme daytime temperatures on hot (summer) days might have affected patterns temporarily. The desired temperature was gradually lowered from 22ºC to 18ºC (range of comfort


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temperature) during the growth period, however higher temperatures could have been expected. Single days with high temperatures deviating from the desired level could possibly have increased water intake and decreased feed intake temporarily (Ingram et al., 1980; Mount et al., 1971; Feddes et al., 1988, 1989; Xin and DeShazer, 1992). Days with high peak temperatures could most likely have been represented in data from batch no. 3 and 6 as these were recorded during summer peri-ods. The results not showing any batch (seasonal) effect could suggest that temporarily peaks of high temperatures would only have increased residual variation rather than have a significant im-pact on mean levels over many days. Such an argument also supports the idea that measurements of the ambient (indoor) temperature could have improved model specification in this study, with a subsequent decrease in the residual variance. Fixed effect associated with pen nos. was only statistical significant (P=0.02) regarding the ‘wa-ter/feed’ ratio, but a similar pattern was not found in the separate analyses of water or feed con-sumption curves (P=0.13 and P=0.12, respectively). The results showed that systematic variability between pens was less pronounced than expected, however the patterns could also have been blurred by random variation in data. Therefore, according to the marginal significance/non signifi-cance levels, no solid conclusions could be drawn. However, the reliability of water measurements was subject to some concern as the FarmWatch water-monitoring system was originally designed for detection of short time changes rather than measurements of absolute values. Also group sizes of measurement were much smaller than normal (levels of individual pens rather than housing sec-tions). An argument against this would be that the water meters used were more accurate (150 digi-tal signals/litre) than the normal type (1 signal/litre). However this question was mainly related to interpretation of specific measurements between water meters as some systematic measurement error could have been expected. There are basically two obvious explanations for this similarity in measurements between pens. Either that the accuracy of water recordings were more reliable than expected thus showing no difference between levels of water consumption between pens. Secondly it could have been caused by random noise in data concealing any effect associated with the indi-vidual pens. As previously mentioned the confounded ‘effect’ of different breeds could also have affected pen specific measurements. The fact that ‘pen’ effect in contrast was significant regarding the ‘water/feed’ ratio could have been caused by opposite effects of water and feed consumption according to the specific pens. This pattern was difficult to explain from a biological point of view. But the results could ‘weakly’ sug-gest a theory of different ‘water/feed’ ratios preferred by different breeds of pigs. This was as the pure breed animals in this study were allocated similarly between pens in different batches (de-scribed in section 3.1), thus confounding the results. Such judgement would need a more detailed analysis than this study provides, so final conclusions cannot be drawn. Another cause could be that although physical conditions between pens were considered to be equal, some systematic effect of


67

being in a particular pen was present, however such differences were not sufficient to affect water or feed intake patterns separately. It could be argued that parameters should have been chosen dif-ferently, ‘pen’ as a random effect and ‘breed’ as fixed effect. But with five combinations of breed not allocated randomly between eight pens this was considered pointless. Although live weight of pigs within pens and more importantly, average live weights between pens were considered to be similar, such variation appeared to influence levels of feed intake between time series. The same influence of live weight at the start of data recordings was not found on either water intake or ‘water/feed’ ratio. There was nothing suspicious about these findings, as it showed that only patterns of feed intake over time were affected by variations in average live weight bet-ween groups of pigs (P<0.01). The mean LW was 24.75 kg (s.d. 1.86 kg) at start of the time series. According to the general increase in water consumption over time (figure 6.1) a similar effect could have been expected in the analysis of water consumption separately, however this lack was possibly related to the high residual variance in this analysis. The results obtained from this study are associated with several limitations regarding adaptability to practical conditions. In the data analysis of this study any incidences of odd character have been excluded. This ensured that the focus stayed on ‘normal’ situations. Therefore in situations when several pigs were removed from the pens, vaccinations, invalid water recording etc. (see appendix A) data was excluded. Medical conditions can cause significant influences of both water and feed intake as described in section 2.5.3. Most commonly feed intake is increased in such situations, whereas water intake could be affected in either ways. Therefore, further investigations of such an impact on water and feed intake patterns would be desirable, if the aim was to use knowledge about water consumption in groups of pigs to estimate feed intake. Further attention towards odd inci-dences such as failure in ventilation systems, water supplies or feeding systems would also be re-quired, as these would disrupt general levels and patterns of the ‘water/feed’ ratio. The data analysis and literature review have focussed on pigs being dry fed and kept indoors, in mechanically venti-lated buildings while eliminating some impacts of climatic variations. Therefore the results of this study may not be adaptable to more extensive production systems.

4.1 Conclusions The overall results from this discussion chapter and this report in general are present in this section. The objective of this study was to investigate expected patterns of, and consistency in patterns of ‘water/feed’ ratio in groups of slaughter pigs. From the data analysis of this study and from the literature reviewed it has not been possible to find a consistent diurnal pattern of ‘water/feed’ ratio for growing pigs. Both water and feed intake pat-


68

terns have been reported to follow distinct diurnal patterns in the literature, however these varied in structure and were dependent on several physiological and environmental conditions. Explorative data analysis revealed that pigs in groups of 14, which were kept under homogenous and strictly controlled conditions did not show consistent diurnal patterns of the derived ‘water/feed’ ratio on a day-to-day basis or between groups. From the results of this study it is concluded that an appropri-ate time interval for accumulation of water and feed intake data in order to analyse patterns of the combined ‘water/feed’ ratio was 24 hours. As considerable day-to-day variation, were found par-ticularly in the water data, time scales longer than 24 hours could also be suggested. An unfortunate consequence of this would be that the exclusion of a period of data, would constitute a larger loss, as some of the lost data may not be invalid. Additionally, if the future aim was to develop a dy-namic model then longer intervals would not be desirable, however this topic has not been in focus in this study. Specific conditions influencing water and feed intake patterns are state of the animals (e.g. age, breed and sex), social factors (i.e. competition levels) and environmental conditions (climate, light-ing, housing, etc.). These conditions have an impact within various time frames, which needs to be considered when choosing day length as an appropriate time interval. It is concluded from the literature that age and sex influence daily levels of water and feed intake, while breed differences are mainly related to diurnal variation in patterns. Age related changes were reported in literature as meal frequency declines while intake rate and meal sizes increase. Such patterns also appeared in the preliminary data analysis section of this study as feeder occupation declined with increasing age. In the data analysis of this study logarithmic transformed values of the ‘water/feed’ ratio could be described with a 2nd order polynomial function describing mean values, although the model comprised random intercepts between time series. Therefore, mean curves be-tween groups of pigs varied in levels. The coefficient of variation between groups was approxi-mately 9%, if a fixed ‘pen’ effect was eliminated. The overall results indicated that the mean ‘water/feed’ ratio (within time series) was rather con-stant for the first 35 days after insertion to the building at 25 kg LW (until approx. 50 kg LW) be-fore then gradually declining from approx. 3.1 l/kg to 2.6 l/kg. Such a declining pattern of the ‘wa-ter/feed’ ratio over time has not been reported in the literature recently, however an older study by Pieterse (1963) showed similar results. It is possible that the decreasing ‘water/feed’ ratio was partly a response to the fastest growing pigs leaving the pens, however under traditional farming conditions with all in–all out production systems this pattern would always be evident, as pigs are gradually removed for slaughter.


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According to the literature environmental factors comprise of several conditions, as some caused secondary responses of feed and water intake through impacts on competition levels. Competition levels appeared to be secondarily influenced by several factors of a more primary nature, such as combinations of group sizes, feeder and drinker allocations, housing designs, etc. Generally, in-creased competition between group members only affects diurnal patterns of water and feed intake, however severe restrictions in feeder or drinker access could change total daily intake of feed and water. Constrictions in feeder or drinker access were considered not to be affecting the total daily intakes of feed or water in the data analysis of this study. The literature stated that another environmental factor of a more primary character was climate, as extreme lower and higher ambient temperatures would affect daily levels of both water and feed consumption. Such a parameter was not measured in the field data analysed in this study, thus caus-ing lack of model performance, in terms of a higher residual variation. A less important factor is the impact of light as the literature states this is expected to mainly affect diurnal consumption patterns. The literature also showed that other factors affecting daily levels of water and feed consumption are feed composition, human activity, health problems, and feeder and drinker designs. Generally, feed composition affected daily levels of ‘water/feed’ ratio as water content and nutritional compo-sition influence the voluntary water intake in proportion to the feed intake. Impacts of human activ-ity could be stimulating or disturbing effects, of which the latter, would have adverse effects on feed and/or water intake. Feeder and drinker designs could influence competition levels between pigs, however, differences in feed or water spillage could be related to specific designs. Therefore wasted feed or water would need to be included in measurements. As previously described housing (pen) conditions were considered to be homogenous between groups in the data analysis of this study, thus such impacts did not significantly affect the results. Impacts of health problems and other odd incidences have not been investigated in detail in this study. However further attention to this aspect would be beneficial, if the overall results from this study were to be used in the development of new methods to link measurements of water intake to feed consumption patterns between groups of pigs.

Chapter 5 Future perspectives ________________________________________________________________________________

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5 Future perspectives This project was stimulated by a desire to provide new information that could be useful in the de-velopment of new tools for improved management in animal production. Thus, a more advanced dynamic model capable of providing information on the distribution of feed consumption between groups of pigs by means of monitoring water intake would be desirable. Accordingly, the general results of this study on the consistency in patterns of the ‘water/feed’ ratio, would suggest that the following parameters were recorded on a daily basis:

- Age of the pigs - Ambient temperature - Average live weight at insertion to the housing section (only at the start of time series)

However, special attention also should be paid towards standardised conditions between groups of pigs, regarding the factors listed below. - Homogenous groups of pigs (according to age)

- Housing conditions (incl. feeder and drinker designs) - Feed composition

- Feeder and drinker access (group sizes vs. feeder and drinker allocation) - Sex of the pigs (not mixed within groups) - Health conditions - Odd incidences (failure in technical systems; e.g. ventilation, heating, feeding systems) If the conditions the different groups of pigs are exposed to differ, then further analysis of such im-pacts on the daily water and/or feed consumption would be required. If measurements of average live weight within groups of pigs continuously were available, then such information could be relevant to consider. Additionally, the information on weight gains over time could possible elucidate some impacts of health related problems also affecting water and/or feed intake.

References 71 ________________________________________________________________________________

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Chen (1991) Modelling eating behaviour of growing finishing swine. Transactions of the American Society of Agricultural Engineers 34:591-596. McDonald, P., R.A. Edwards, J.D.F. Greenhalgh and C.A. Morgan (1995) Animal Nutrition. 5th edition. Addison Wesley Longman Ltd. UK. McDonald, L.M., J. Crane, A.H. Stewart, S.A. Edward and P.R. English (1996) The effect of drinking through space on the performance and behaviour of growing pigs in large groups on deep-bedded straw. Animal Production 62:677-678. Meyer, K (1998) Estimating covariance functions for longitudinal data using a random regression model. Genetics Se-lection Evolution 30:221-240. Morgan, C.A., G.C. Emmans, B.J. Tolkamp and I. Kyriazakis (2000) Analysis of the feeding behaviour of pigs us-ing different models. Physiology and Behaviour 68:395-403. Mount, L.E., C.W. Holmes, W.H. Close, S.R. Morrison and I.B. 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Whittemore (1996) Effect of single space feeder design on feeding behaviour and performance of growing pigs. Animal Production 62:677. Nielsen, B.L., A.B. Lawrence and C.T. Whittemore (1996) Feeding behaviour of growing pigs using single or multi space feeders. Applied Animal Behaviour Science 47:235-246. Nienaber, J.A. and G.L. Hahn (1982-F12) Heat production and feed intake of ad libitum fed growing swine as af-fected by temperature. American Society of Agricultural Engineers 82:195-202. St. Joseph MIASAE. Nienaber, J.A., T.P. McDonald, G.L. Hahn and Y.R. Chen (1990) Eating dynamics of growing finishing swine. Transactions of the American Society of Agricultural Engineers 33:2011-2018. Patterson, D.C. (1985) A note on the effect of individual penning on the performance of fattening pigs. Animal Pro-duction 40:185-188. Petersen L.B. (1995) Drikkekoppen ”Drik-o-mat” kontra bideventiler til slagtesvin. In: Infosvin, Svinefaglig database. Landsudvalget for Svin, Den rullende Afprøvning. 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Stryhn, H., I. Skovgaard and M. Rudemo (1997) Statistisk Grundkursus Bind 1, Studieudgave. DSR Forlag, Køben-havn: 195-198. Suevia (2002) Product information page (Suevia model 96) at http://www.suevia.com. Thorup, F. (1992) Brunstforhold hos sopolte. Notat. Landsudvalget for Svin, Danske Slagterier. Afd. for ernæring og reproduction. Danmark: 1-5. Turner, S.P., S.A. Edwards and V.C. Bland (1998) The influence of drinker allocation and group size on the drinking behaviour, welfare and production of growing pigs. Animal Science 68:617-622. Turner, S.P., A.G. Sinclair and S.A. Edwards (2000) The interaction of live weight and the degree of competition on drinking behaviour in growing pigs at different groups sizes. Applied Animal Behaviour Science 67:321-334. Walker, N (1991) The effects on performance and behaviour of number of growing pigs per mono-place feeder. Ani-mal Feed Science and Technology 35:3-13. Weisberg, S. (1985) Applied Linear Regression. 2nd edition. University of Minnesota, St. Paul, Minnesota, USA:169-185. West, M. and J. Harrison (1997) Bayesian Forecasting and Dynamic Models. 2nd edition. Springer –Verlag New York, USA. Whittemore, C.T. (2000) The practice and science of pig production. Longman Scientific and technical. Xin, H. and J.A. DeShazer (1991) Swine responses to constant and modeified Diurnal cyclic temperatures. Transac-tions of the American Society of Agricultural Engineers. 36(6):2533-2540 Xin, H. and J.A. DeShazer (1992) Feeding patterns of growing pigs at warm constant and cyclic temperatures. Trans-action of the American Society of Agricultural Engineering 35:319-323. Yang, T.S., B. Howard and W.V. McFarlane (1981) Effects of food on drinking behaviour of growing pigs. Applied Animal Ethology 7:259-270. Young, R.J. and A.B. Lawrence (1994) Feeding behaviour of pigs in groups monitored by a computerized feeding system. Animal Production 58:145-152.

Personal Communication Nielsen, T. (2003) Thokild Nielsen, TH Klimateknik A/S. Thorning, Kjellerup, Denmark. Phone +45 86 88 03 65. Maribo, H. (2002) Hanne Maribo, The National Commitee for Pig Production in Denmark. Phone +45 33 73 26 26. Thorup, F. (2003) Flemming Thorup, The National Commitee for Pig Production in Denmark. Phone +45 33 73 26 45.

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Appendix

1 Data validation ............................................................................................................................75 2 Graphs with time series of average water and feed consumption and ‘water/feed’ ratio ...........78 3 Simple statistical model used in preliminary data analysis.........................................................84 4 Orthogonal polynomials..............................................................................................................85 5 First order autoregressive error structure ....................................................................................86 6 Residual plots ..............................................................................................................................87 7 Statistical model reductions ........................................................................................................89

Appendix 1 75

Data validation The table below shows exclusion of invalid data according to data validation based on incidences recorded in logbook and explorative analysis of the individual data series.

Period Excluded Batch Pen no. Days Water Feed

Explanation

1 All <=8 X X Habitation period 1 All 20-21 X Invalid water registrations 1 All 65 X Invalid water registrations 1 All 76-77 X Invalid water registrations 1 1 Whole X (x) Water registrations failed after day 30 1 3 >=90 X X < 3 pigs 1 3 >=83 X X <5 pigs 1 4 <=15 X X Habitation period /diarrhoea treatment 1 4 83 X X 4 pigs removed 1 4 >=90 X X <6 pigs 1 5 <=15 X X Habitation period /diarrhoea treatment 1 5 30-32 X X Unidentified problem – major drop in feed and water consumption 1 5 49 X X Vaccination 1 5 70 X X Vaccination 1 5 >=83 X X <4 pigs 1 6 <=15 X X Habitation period /diarrhoea treatment 1 6 >=90 X X <3 pigs 1 7 >=95 X X <7 pigs 1 8 >=90 X X <4 pigs 2 All <=7 (x) X Habitation 2 All <=25 X Invalid water registrations/habitation 2 All 30 X X Unidentified problem - drop feed and increase in water consumption 2 All 41-43 X Invalid water registrations 2 All 57-63 X Invalid water registrations 2 All 91 X Invalid water registrations 2 All 48-51 X X Vaccination 2 1 78 X X 6 pigs removed 2 1 >=80 X X <6 pigs 2 2 78 X X 3 pigs removed 2 2 84 X X <9 pigs 2 3 84 X X <5 pigs 2 4 <=35 X Irregular water registrations 2 4 46-54 X X Strongly affected by vaccination 2 4 78-79 X X 8 pigs removed 2 4 >=84 X X < 4 pigs 2 5 >=84 X X <6 pigs 2 6 Whole X (X) Invalid water registrations 2 7 >=80 X X <5 pigs 2 8 >=92 X X <5 pigs

Appendix 1 76


Explanation

3 All <=7 X X Habitation period 3 All 10-11 X Invalid water registrations 3 All 45 X Invalid water registrations 3 All 59-64 X Invalid water registrations 3 1 17-24 X Invalid water registrations 3 1 67-72 X Invalid water registrations 3 1 >=84 X X <3 pigs 3 2 15-18 X Invalid water registrations 3 2 9 X Invalid water registrations 3 2 45-49 X X Unidentified problem - drop in feed consumption/increase in water 3 2 59-64 X X Vaccination and lack of water registrations 3 2 65-70 X X Unidentified problem - drop in feed consumption/fluctuation in water 3 2 >=82 X X <9 pigs 3 3 54-58 X X Vaccination and lack of water registrations 3 3 >=84 X X <3 pigs 3 4 7-9 X Invalid water registrations 3 4 >=85 X X <5 pigs 3 5 54-58 X X Vaccination and lack of water registrations 3 5 >=92 X X <5 pigs 3 6 >85 X X <4 pigs 3 7 70-73 X X 7 pigs removed 3 7 >=85 X X Pen empty 3 8 <=15 X X Habitation period 3 8 23-25 X X Unidentified problem - previously treated for diarrhoea 3 8 >=92 X X <3 pigs 4 All <=5 X X Habitation period 4 All 24-25 X Invalid water registrations 4 1 >=78 X X <11 pigs 4 2 8-9 X Invalid water registrations 4 2 16 X Invalid water registrations 4 2 76 X X Unidentified problem - drop in feed/increased water (prev. vaccinated) 4 2 >=86 X X Pen empty 4 3 16 X Invalid water registrations 4 3 44-54 X Lack of water registrations 4 3 >=85 X X <7 pigs 4 4 8-9 0 Invalid water registrations 4 4 16 X Invalid water registrations 4 4 <=40 X Problem with blocked drinker 4 4 >=78 X X <12 pigs 4 5 16 X Invalid water registrations 4 5 >=79 X X <13 pigs 4 6 16 X Invalid water registrations 4 6 71-75 X X 8 pigs removed 4 6 >=85 X X Pen empty 4 7 8-9 X Invalid water registrations 4 7 >=85 X X Pen empty 4 7 16 X Invalid water registrations 4 8 8-9 X Invalid water registrations 4 8 16 X Invalid water registrations 4 8 >=79 X X <5 pigs

Appendix 1 77


Explanation

5 All Whole X (X) Serious lack of water data/logbook data not considered 6 All <=7 X X Habitation period 6 All 38-41 X Invalid water registrations 6 All 54-60 X X Vaccination and problem with water registrations 6 All 65 X Invalid water registrations 6 All 77-78 X Invalid water registrations 6 1 78 X X 4 pigs removed 6 1 >=92 X X <3 pigs 6 2 >=92 X X <3 pigs 6 3 Whole X (X) Invalid water registrations 6 4 >=84 X X <10 pigs 6 5 84 X X 4 pigs removed 6 5 >=92 X X <4 pigs 6 6 >=92 X X <4 pigs 6 7 >=78 X X < 2pigs 6 8 78 X X 6 pigs removed 6 8 >=85 X X <4 pigs

Appendix 2 78

The diagrams show development in average figures of daily water consumption (red), daily feed consumption (green) and ‘water/feed’ ratio (blue) for each time series.

Batch no. 1 (13.09.2000 – 19.12.2000)

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Appendix 2 79 Batch no. 2 (30.01.2001 – 08.05.2001)

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Appendix 3 84

Simple statistical model used in the preliminary data analysis In the preliminary data analysis a first simple statistical model was established. This was a simple co-variate model assuming independency of variation between single observations: Yijk = β0 + αi + γj + β1tijk + (αγ)ij + (αβ1)itijk + (γβ1)jtijk + (αγβ1)ijtijk + εijk

where: Yijk ‘water/feed’ ratio i = batch no.1, 2, 3, 4, 6 j = pen no.1, 2, …, 8 tijk time of observation i,j,k αi = fixed effect of batch γj = fixed effect of pen β0 overall intercept β1 regression parameter - co-variate and interactions according to the model εijk ~ N(0,σ2), independent of each other Experimental unit ~ batch*pen

In this first simple model all effects were assumed being fixed. The output of the SAS mixed model procedure, showed that all effects and interactions in the model were significant, not enabling any model reduction. An extended polynomial model with day squared was also analysed with similar results, all effects and interactions being significant. The two graphs in figure 1 show residual plots from the model as presented with either raw or loga-rithm transformed values.

Resi d

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Figure 1 Residual plots with model applied to raw values and logarithm transformed values respectively (Studentized residuals plotted against predicted values).

The outlay of the residual plots did not indicate any suspicious pattern or funnel shape indicating that the investigation of the untransformed data was inappropriate. Therefore the Cook’s influence statistics were based on raw values rather than on transformed values of the ‘water/feed’ ratio.

Appendix 4 85

Orthogonal polynomials (estimation)

If two variables X1 and X2 are orthogonal then the regression of Y on X1 is identical to the regres-sion of Y on X1 ignoring X2 (Weisberg, 1985). Orthogonality implies that the correlation between X1 and X2 is zero. In order to estimate orthogonal polynomials for this study the following condi-tions should be met:

( ) ( ) 0max

0=∑

=

t

tji tXtX ; t = 0,1,2…, tmax and i ≠ j (Snedecor and Cochran, 1989)

<=> , , and ∑ ( ) ( )∑=

≅max

010 0

t

ttXtX ( ) ( )∑

=

≅max

020 0

t

ttXtX ( ) ( )

=

≅max

021 0

t

ttXtX

where X0(t) = C1 (C1 a constant ≠ 0)

Linear component: X1(t) = t – C2

Quadric component: X2(t) = (t-C2)2 – C3

Figure 1 shows how values of C2 and C3 corresponds each other when the red and yellow areas equal each other. (C2 is a constant describing the mid point of the average length of time series’)

Figure 1 Values of C2 and C3 is estimated so that the red and yellow areas equal each other respectively (C2=0 implies that data have been centered)

In the analyses of this study, the two orthogonal polynomials of interest were estimated as follows:

X1(tijl) = t-49 and X2 (tijl) = (tijl-49)2-851

Appendix 5 86

First order autoregressive error structure

A first order autoregressive error structure as commonly used in time series analysis (Crowder and Hand, 1990) is shown below. et = ρet-1 + ut, for t>2 ρ is the regression parameter describing the autocorrelation, and ut are the innovation error usually assumed to be N(0,σ2

u). Repeated applications for et-1, et-2,……, yields

∑−

=−=

1

0

t

nnt

nt ue ρ = ut + ρut-1 + ρ2ut-2 + … + ρt-2u2 + ρt-1u1 for t = 1,2…tmax

Thus the model error is a linear combination of independent normally distributed errors in the ex-pression of the first formula. The u values that have the greatest impact on et are those disturbances that are most recent. Since the ut’s are independent it follows that:

E(et) = 0 and ∑−

=

=1

0

22)(t

n

nuteVar ρσ

The expression can also be written as 1/(1-ρ∑∞

=0

2

n

nρ 2).

Thus, for large t

−

≅ 22

11)(ρ

σ uteVar

And in a similar fashion:

−

=+ 22||

11),(ρ

σρ un

ntt eeCov

Yielding: ( ) 2

2

2

2

1.....1.1.1

,ρ

σρρ

ρρρρ

−

= ueeCov

In SAS the autoregressive process is denoted by type=AR(1).

Appendix 6 87

Residual plots Top plots within each category of analysis represent residual plots from untransformed data, whereas the plots below represent residual plots from logarithmic transformed data. Plot at left are standardised residual values plotted against time (day) of observation. Plots at the right side show standardised residual values plotted against predicted values according to the fixed part of the model (method described by Hox (2002)). Water

Resi dual pl ot unt ransf ormed dat a

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Appendix 6 88

Feed Resi dual pl ot unt ransf ormed dat a

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‘Water/feed’ ratio


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0. 940. 950. 960. 970. 980. 991. 001. 011. 021. 031. 041. 051. 061. 071. 081. 091. 101. 111. 121. 131. 14

Appendix 7 89

Statistical model reductions Water Step Description/TEST Trait Parameter estimate Test value Model reduction

1 β3=0

Cubic regression coefficient

- P=0.34 YES

2 B2ij=0

Random quadratic coefficient

σ2B2ij ≈ 0 N/A YES

3 eijl - σ2uijl = 0.008027

ρ = 0.9393 G2 =573.2 ~ χ2(2) (P<0.0001)

NO

4 εijkl=0

- σ2ε1ijkl=0.006214 G2 =262.9 ~ χ2(1)

(P<0.0001) NO

5 B1ij=0

Random coefficient σ2B1ij~0 AIC -4,148.6 =>

AIC –4,149.7 YES

6 Ai=0

Random batch effect σ2Ai=3.4x10-39 => AIC -4.149.7 YES

7 α=0

Regression coefficient (live weight)

- P=0.14 YES

8 γj=0

Fixed pen effect - P=0.13 YES (final model)

9 B0ij=0

Random intercept σ2Bij=0.01058 AIC -4,163.1 =>

AIC -4.144.5 NO

Start Yijkl = (β0 + B0ij) + Ai + γj + αWij+ δk(i,j.l) + (β1 + B1ij)X1(tijl) + (β2 + B2ij)X2(tijl) + β3X3(tijl) + β4X4(tijl) + eijl + εijl Final Yijkl = (β0+B0ij) + δk(i,j.l) + β1 X1(tijl) + β2X2(tijl) + eijkl + εijkl

Feed Step Description/TEST Trait Parameter estimate Test value Model reduction

1 B2ij =0 Random quadratic coefficient

σ2B2ij ≈ 0 N/A YES

2 B1ij =0

Random gradient σ2B1ij=2.2x10-9 AIC –3,810.1 =>

AIC –3,797.2 NO

3 eijl = 0 - σ2uijl = 0.004495

ρ = 0.7831 G2 =145.8 ~ χ2(2) (P<0.0001)

NO

4 εijkl=0

- σ2ε1ijkl= 0.009059 N/A NO

5 Ai = 0 Random batch effect σ2Ai=0 AIC –3,810.1 =>

AIC –3,810.1 YES

6 γj=0

Fixed pen effect - P=0.12 YES (Final model)

7 β3=0 Cubic regression coefficient

- P=0.04 NO

Start Yijl = (β0 + B0ij) + Ai + γj + αWij+ (β1 + B1ij)X1(tijl) + (β2 + B2ij)X2(tijl) + β3X3(tijl) + β4X4(tijl) + eijl + εijl Final Yijl = (β0+B0ij) + αWij + δk(i,j.l) + (β1+B1ij)X1(tijl) + β2X2(tijl) + β3X3(tijl) + eijkl + εijkl

Appendix 7 90

‘Water/Feed’ ratio Step Description/TEST Trait Parameter estimate Test value Model reduction

1 β3=0

Cubic regression coefficient

- P=0,17 YES

2 B2ij =0


σ2B2ij = 0 AIC -4558.1 =>

AIC -4,558.7 YES

3 B1ij =0


σ2B1ij = 3.2x10-7 => AIC -4,559.9 YES

4 Ai=0

Random batch effect σ2Ai=0.000558 => AIC -4,561.4 YES

5 eijl=0 - σ2uijl = 0.006801

ρ = 0.9164 G2 =762.4 ~ χ2(2) (P<0.0001)

NO

6 εijkl=0

- σ2ε1ijl = 0.004708 G2 =200.8 ~ χ2(1)

(P<0.0001) NO

7 α=0

Regression coefficient (live weight)

- P=0,27 YES (final model)

8 B0ij =0

Random intercept σ2B1ijkl = 0.006796 AIC –4,562.2=>

AIC -4,557.2 NO

Start Yijkl = (β0 + B0ij) + Ai + γj + αWij+ δk(i,j.l) + (β1 + B1ij)X1(tijl) + (β2 + B2ij)X2(tijl) + β3X3(tijl) + β4X4(tijl) + eijl + εijl Final Yijkl = (β0+B0ij) + γj + δk(i,j.l) + β1X1(tijl) + β2X2(tijl) + eijkl + εijkl

relationships between water and feed intake during the growth … · 2009-09-09 · ratio between...

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