Applied Animal Behaviour Science, 15 (1986) 229--240 229 Elsevier Science Publishers B.V., Amsterdam - -Pr in ted in The Netherlands

EARLY POST-NATAL BEHAVIOUR IN LAMBS OF TEN BREEDS

J. SLEE and ANTHEA SPRINGBETT

A.F.R.C. Animal Breeding Research Organisation, Kings Buildings, West Mains Road, Edinburgh, EH9 3JQ (Gt. Britain)

(Accepted for publication 25 April 1985)

ABSTRACT

Slee, J. and Springbett, A., 1986. Early post-natal behaviour in lambs of ten breeds. Appl. Anita. Behav. Sci., 15: 229--240.

Activity and sucking behaviour during the first hour after birth, and rectal temperature were recorded in 297 lambs of 10 breeds: Scottish Blackface, Welsh and Cheviot (hill breeds); Oxford, Border Leicester, Southdown, Merino and Finn (lowland); Soay and Boreray Blackface (feral).

Two components of behaviour were analysed; the time to stand following parturition and the time to reach the udder. There were significant breed differences in both com- ponents. Lambs stood for at least 3 min during the first hour except for about half the Leicesters and most Finns. The feral and hill breeds and the Oxfords reached the udder early; the remaining breeds were slow or unsuccessful. Failure to reach the udder was associated with a higher incidence of hypothermia, especially in Finns and Merinos.

Weather (combined air temperature and windspeed) was correlated with udder-seeking success but not with the time to stand.

Within breeds, birthweight affected the times to stand and reach the udder, but litter size did not, except through its effect on birthweight.

The present results and other data from the same breeds showed that those breeds with effective udder-seeking behaviour also tended to have good resistance to hypothermia and low perinatal mortality.

INTRODUCTION

In order to survive, a newborn lamb should stand, suck from its mother and establish a bond with her as soon as possible after birth. The maintenance of a normal body temperature is also necessary if the lamb is to be mobile (Slee, 1977) and find the udder and suck {Alexander and Williams, 1966a, b). The ability to withstand cold-exposure, as well as being necessary to avoid lethal hypothermia, may also be important in establishing a secure maternal bond with adequate suckling. If exposure to cold disrupts the behaviour patterns necessary to ensure suckling, as reported by Alexander and Williams (1966a, b), then energy reserves, being depleted by the demand for increased heat production, will not be replenished and the lamb will

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die from cold and starvation (Slee, 1979, 1981). The cold/starvation syndrome is frequently the major cause of early post-natal lamb mortali ty (Houston and Maddox, 1974).

Previous work showed that lambs of different breeds varied significantly in their ability to resist hypothermia and in their field mortal i ty rates in the same location (Sykes et al., 1976; Slee et al., 1980). The present work involved detailed observations on the neonatal behaviour of lambs of the same breeds born under similar conditions at the same location. The breeds differed in the following respects: (i) the environments to which they were previously adapted; (ii) their natural lamb mortal i ty rates; (iii) their suscep- tibility to hypothermia; (iv) physical characteristics such as birthweight, coat type and litter size.

The breeds could be broadly classified as: commercial hill sheep, lowland sheep (both large and small) and feral sheep. Comparisons between these main types, which would presumably have been subjected to different selection pressures for lamb viability, could be valuable in identifying genetic variation in components of behaviour relevant to survival. For example, the two feral breeds (taken from St. Kilda where there is a high lamb mor. tality rate, Jewell et al., 1974) would have been adapted to a situation of severe climatic and nutritional stress. Lowland commercial sheep, with the advantages of shelter, shepherding and adequate nutrition, would have been subjected to different types of selection.

The behavioural observations covered the first hour after birth, during which time most lambs stand and begin to suck (Alexander, 1958; Bareham, 1976). The events observed included activity immediately after birth, dam-directed behaviour and sucking behaviour, and were similar to those described by Bareham (1976) in Clun Forest and Suffolk cross lambs born indoors. Lamb body temperatures and prevailing weather conditions were also recorded, so that interactions between breeds, weather severity, sus- ceptibility to hypothermia and early behaviour could be considered. This investigation was expected to indicate which aspects of early neonatal behaviour might be important components of survival.

MATERIALS AND METHODS

Observations were carried out on an Animal Breeding Research Organisa- tion (ABRO) lowland farm at the Dryden Laboratory, Roslin, Midlothian, between 1975 and 1978. During those years, 860 ewes of 10 breeds lambed. Scottish Blackface (202); South Country Cheviot (81); Welsh Mountain (117); Oxford Down (38); Border Leicester (50); Southdown (57); Finnish Landrace (94); Tasmanian Merinos (87); Soay (109); Boreray Blackface (25).

The sheep were bred at Dryden bu t derived originally from different sources. The Scottish Blackface and Welsh Mountain breeds were from

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A.B.R.O. hill farms in Tweeddale and in North Wales, respectively, the Cheviots and Border Leicesters were from the South of Scotland, the Oxfords from an A.B.R.O. lowland farm in Staffordshire, the Southdowns from the South of England, and the Finnish Landrace from an A.B.R.O. upland farm in Tweeddale. The Boreray Blackfaces and Soays were im- por ted by A.B.R.O. in 1966 and 1970, respectively, from feral sheep popula- tions on the island of St. Kilda, 100 miles of f the west coast of the Scottish mainland, and the Tasmanian Finewool Merinos were imported by A.B.R.O. f rom Australia in 1956.

Lambing usually began in January or February and continued until May or June. The ewes lambed under natural conditions in either a 0.2-ha pad- dock containing up to 8 sheep, or a 1.2-ha field containing up to 30 sheep. Observations were conducted outdoors from 08.30 until 18.30 on week- days, if daylight permitted, and from 09.30 until 16.30 at weekends. The sheep were viewed from nearby laboratory windows or from inside a caravan. Births which occurred overnight or which were not actually observed were excluded, and so were observations where there was any disturbance or interference. This procedure resulted in acceptable observations on 297 lambs (see Table I).

TABLE I

Lambs observed over 4 years with average littersize and birthweight

Breed Breed No. of lambs Mean Range Mean type litter-size birthweight (kg)

S. Blackface Hill 69 1.4 (1--2) 3.6 Welsh 63 1.7 (1--3) 2.8 Cheviot 20 1.4 (1--3) 3.7

Soay Feral 28 1.4 (1--2) 1.8 Boreray 9 1.1 {1--2) 2.5

Oxford Lowland 13 1.3 (1--2) 5.9 B. Leicester 24 1.8 (1--4) 4.3 Southdown 22 1.4 (1--2) 3.5 Merino 16 1.1 (1--2) 3.5 Finn 33 2.5 (1--4) 2.3

Total 297

The following observations were made on the lambs and were t imed from the complet ion of the birth process: first shaking of head; first a t tempt to rise on knees; first a t tempt to rise on feet; standing for 1 min; standing for 3 min; nudging along the flanks of the ewe; nudging the ewe in the udder region; lamb first at the udder; apparent sucking.

Observations generally continued for 1 h after birth, or until the lamb sucked, whichever occurred first.

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Observations on lambs which did not suck within 1 h were therefore truncated. In addition, lambs which lay immobile for more than 25 min in cold weather were considered to be in danger of hypothermia and un- likely to suck. They were removed and brought indoors. Incomplete obser- vations thus arose from 1-h truncation or early removal.

Lamb rectal temperatures were measured after 1 h when observations were completed, or when suspected hypothermic lambs were removed and brought indoors. The latter were measured at the time of removal (usually between 30 and 50 min after birth). Sykes et al. (1976) showed that the rectal temperatures of lambs in the field change little between 20 min and 1 h after birth, so the measurements should be comparable. Measure- ments were obtained from a thermoelectric dial thermometer (Light Lab- oratories) with a thermistor probe inserted 6 cm (Sykes et al., 1976). The weather was also recorded as follows: air (shade) temperature; wind speed (from a cup anemometer placed 25 cm above the ground); sun (presence/ absence); rain (absent, moderate or heavy). In the data analysis, weather conditions were represented by an index of the cooling power of the en- vironment, derived from the air temperature (°C) and the wind speed, according to tables published by Burton and Edholm (1955). The index was calculated by reducing the measured air temperature by 2--16°C for wind speeds varying from 0.2 to 6.7 m s -1. This index was termed "effective ambient temperature" (EAT). Temperature and air movement were likely to be the most important components affecting the cooling power of the environment upon a newborn lamb already soaked by amniotic fluids. The relationship between EAT and the cooling power of the environment was tested by reference to a simple artificial lamb constructed from a 12 X 21 × 23-cm tin box containing a 60 W light bulb as a heat source and a thermostat , lined with 1-cm thick polystyrene and covered by a lamb's skin. The ther- mostat was set to maintain the surface of the box at 30°C (a typical skin temperature) and was connected to an electric meter and power supply. When the box was exposed to different weather conditions in the field, ranging from -3 to +10°C EAT, a very close linear relationship (r = -0.97, P<0.001) was found between EAT and the power required to maintain the box surface temperature at 30°C (Slee, 1977). The power required at 0°C EAT (30 W) was equal to that calculated by Alexander (1974) to be required for a 3-kg lamb to maintain homeothermy at 0°C. EAT therefore gave a good estimate of the cooling power of the environment over a range of weather conditions upon an object generating about the same amount of heat as a young lamb.

Statistical analysis

Performance was measured by the time taken to complete events in the sequence, from the first struggle to rise until apparently sucking. Three events were analysed in detail: " t ime to first stand"; "standing for 3 min";

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"at udder". These were chosen because they showed considerable variation between lambs, were well defined, and represented both early activity and, probably, success in establishing a maternal bond with suckling.

Breed, birth type, birthweight, sex, date of birth, EAT and time of birth were used as covariates in the main analysis. The Boreray and Soay breeds were combined into one feral breed because of the small numbers available. Due to incomplete records, the analyses were based on 244, 264 or 297 lambs, depending on the event being studied. Lambs which had truncated values for some events because of early removal or time expiry, were given approximate times by the use of two different formulae. For lambs removed early: time (i) = 80 + 10 (i-j)

where i is the number of the event under consideration and j the number of the event at which the lamb was first truncated.

For lambs following time expiry: time (i) = 70 + 5 (i-j) with i and j as above.

Five was used as an increment for truncated observations because 5 min was the average time between completion of successive events after 60 min for a special group of 24 lambs which was observed for longer than 1 h. Most of the lambs removed early were Finns. Due to the dissimilarity between the Finns and the other breeds, the data were analysed both including and excluding Finns. When they were excluded, many fewer lambs with approximated times entered the analysis, but there was little effect on the results. The data were transformed to logarithms to make the distribution closer to a normal dis tr ibut ion and then subjected to least-squares analysis (Harvey, 1972).

RESULTS

The number of lambs of each breed, with litter size and birthweight, are shown in Table I. Noteworthy features are the high litter size of the Finns, the low birthweight of the Soays and Finns, and the high birth- weight of the Oxfords.

Table II shows lamb rectal temperatures and the prevailing weather (ex- pressed as the effective ambient temperature). The feral breeds encountered warmer weather than the other breeds.

Table III shows the number of lambs with full records available for analysis, the incidence of premature removal, and the proportion of lambs in each breed that reached the udder within 1 h of birth. Fewer lambs were available here than are recorded in Table I because some with incomplete records due to early removal were omit ted from parts of the analysis. Lambs removed during observations were immobile (often in bad weather) and unlikely to have sucked. Many of these lambs, particularly Finns, were found to be hypothermic (Table II). Twenty (71%) Finns were removed early compared with five (26%) Leicesters and only three out of all the other breeds combined. Some Border Leicesters were immobile wi thout

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TABLE II

Mean (± SE) rectal t empera tu re and mean effect ive ambien t t empera tu re (EAT) for lambs 1 h af ter bi r th or when removed during the first hour

All lambs EAT Lambs removed early (adjusted)

Numbe~ Rectal (° C) Number Rectal t empera tu re t empera tu re (°c) (°c)

S. Blackface 56 39.6 ± 0.5 0.9 0 - - Welsh 49 39.3 ± 1.6 -1 .4 0 - - Cheviot 26 39.7 ± 1.2 0.5 1 35.6 Soay 25 39.2 ± 1.6 4.8 2 35.0 Boreray 8 39.5 ± 0.4 8.0 0 - - Oxford 9 39.3 ± 0.5 -2 .7 0 - - B. Leicester 20 37.7 -+ 2.8 0.1 5 37.4 ± 1.0 S o u t h d o w n 22 37.2 ± 2.0 -1.1 0 - - Merino 16 34.7 ± 4.6 0.6 0 - - F inn 33 33.2 _+ 3.7 -1 .4 20 31.9 ± 3.5

All breeds 264 38.1 ± 3.1 29 33.2 ± 3.7

1Some of the lambs present in Table I were omi t t ed because o f incomple te records. Standard errors for EAT means varied be tween 0.2 and 1.4.

TABLE III

F r equency of lambs able to s tand and reach the udder or r emoved early wi th in 1 h of bir th

Num ber P ropor t ion P ropor t ion P ropor t ion P ropor t ion P ropor t ion of o f lambs of lambs of lambs of lambs of lambs lambs' s tanding s tanding removed reaching observed

(%) for 3 rain before 1 h udder for 1 h bu t (%) (%)5 wi th in 1 h failing to

(%) reach udder (%)

S. Blackface 55 100 100 0 93 7 Welsh 47 98 96 0 92 8 Cheviot 20 95 90 (5) 85 (10)

Soay 31 100 97 6 94 0 Boreray Oxford 9 100 89 0 89 (11) B. Leicester 19 74 58 26 42 32 S o u t h d o w n 21 100 95 0 38 62 Merino 14 100 93 0 21 79 F inn 28 57 29 71 0 29

Number of lambs wi th comple te records for analysis. ~Lambs removed were immobi le and suspected to be hypo the rmic . Some percentages (in parentheses) are based on very few lambs.

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being hypothermic, whereas Merinos tended more of ten to be hypothermic wi thout immobili ty. Figure 1 shows the distributions of rectal temperature of lambs which reached or failed to reach the udder. Tables III and V show that there were large and significant breed differences in the proport ion of lambs removed or failing to reach the udder, and there is an indication from Table II and Fig. 1 that lambs in these classes were hypothermic -- particularly the Finns and Merinos.

Table IV shows average times to stand and reach the udder for lambs of each breed. These measurements represented early activity and udder- seeking ability. There were significant (P<0.01) differences between breeds in the time taken to stand for 1 min and for 3 rain (Table V). Variation in birthweight within breeds significantly influenced the time to stand for 3 min (light lambs were slower; P<0.05) , but litter size did not, except indirectly through its effect on birthweight. Between breeds, on the other

60 (o)

50

~,o LAHBS FAILING TO REACH UDDER

(n=76) 30

20

~ua 0 25 2'7 21~ 29 31) ~I 3'2 33 31. 3~ 36 3'/ 3~ 39 ~b ~i 42 '

60

(b)

5O

~o I LAMBS REACHING UDDER ] I ( n = l @ 8 )

2O

0 26 27 2B 29 30 31 32 33 3i. 35 36 37 ]B 99 &0 z,.1 /~2

RECTAL TEMPERATURE ( °C )

Fig. 1. Percentage frequency distribution of rectal temperatures measured about 1 h after birth for lambs (a) failing or (b) succeeding in reaching the udder. Lambs removed early (immobile and considered unlikely to reach the udder) are included in (a).

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hand , those which were slow to s tand t e n d e d to be heavy (Leicester and Oxfo rd ) or were member s o f large li t ters (Finns) . The feral and Blackface lambs, which s tood quickly , were o f light or m e d i u m weight . Bir thweight had less e f fec t on the behaviour o f single lambs than o n multiples. This is ev ident in a significant b i r thweight X b i r th - type in te rac t ion (Table V) and f r o m significantly d i f f e ren t regression slopes relat ing b i r thweight to t ime t o s tand in singles and twins.

TABLE IV

Fitted mean times required for lambs to stand and reach the udder

Breed Number of lambs Time to stand Time to reach at start ~ for 3 min (rain) udder (rain) 2

S. Blackface 55 17.5 30.9 Welsh 47 19.2 24.3 Cheviot 20 24.0 35.8

Soay 31 17.7 30.9 Boreray Oxford 9 27.2 31.2 B. Leicester 19 29.6 56.1 Southdown 21 20.1 53.8 Merino 14 19.3 72.6 Finn 28 54.0 94.6

Some of the lambs present in Tables I and II were omitted because of incomplete records. 2Incorporating some estimated times (see Methods).

There were significant b reed d i f ferences in the t ime t aken to f ind the udde r (Tables IV and V), wi th the Welsh being the quickest , fo l lowed by the feral breeds , t he Blackface and the Oxfo rd . The S o u t h d o w n , Border Leicester , F inn and Merino were clearly s lower than the o th e r breeds.

There was a cor re la t ion (r = +0.48, P < 0 . 0 0 1 ) be tween the t ime to s tand for 3 rain and t ime to f ind the udder . However , the f o r m e r was n o t a reliable p red ic to r o f subsequen t udder- locat ing success; fo r example , b o t h the Merino and S o u t h d o w n were relat ively quick to s tand b u t slow or unsuccess- ful in locat ing the udder . I f success in reaching the udde r (Table III) and the t ime t aken to do so are cons idered toge ther , t h en the re is a fair ly clear d is t inc t ion be tween the hill and feral breeds plus the Oxfords , which per- f o r m e d well, and the remaining lowland breeds which p e r f o r m e d badly . Within breeds and b i r th- types , heavier lambs loca ted the udder fas ter (P<0 .01) . Be tween breeds there was no clear re la t ionship wi th weight .

Weather , assessed by EAT, did no t a f fec t t he t ime to s tand, and was t he r e f o r e d r o p p e d f rom the mode l {Table V). However , EA T did have a significant (P <0 .01 ) e f fec t on udde r seeking such t h a t lambs which en- cou n t e r e d cold wea the r were s lower to reach the udder . As shown in Fig. 1,

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T A B L E V

Analys is o f var iance for var iables a f fec t ing t he t ime t a k e n f r o m b i r t h for l ambs to s t and

and f ind t he udde r

Source of var ia t ion df MS F ra t io

Time to f irst s t and for 1 ra in Year 3 0 .108 1.05 Breed 8 0 .478 4 .64*** Sex 1 0 .00672 0 .06 Bi r th - type 1 0 . 0 0 1 0 6 0.01 Year X b reed 23 0 .190 1 . 8 4 " * Year x sex 3 0 .254 2.47 B i r thwe igh t I 1 0 .393 3 .87* Bi r th - type 2 x b i r t h w e i g h t 1 1 .65 1 6 . 0 2 " * * Res idual 242 0 .103 Tota l 283

Time to first s t and for 3 ra in Year 3 0 .276 4 .39** Breed 8 0 .316 5 . 0 3 " * * Bi r th - type 1 0 .0111 0.18 Date 1 0 .0139 0 .22 Breed X date 7 0 .117 1.86 B i r thwe igh t 1 0 .742 1 1 . 8 1 " * * Bi r th - type X b i r t hw e i gh t 1 0 .347 5 .52* Res idual 261 0 .0628 , To ta l 283

Time to reach u d d e r Year 3 0 .244 Breed 8 1.35 Bi r th - type 1 0 .196 B i r thwe igh t 1 0 .381 EAT 1 0 .328 Residual 269 0 .0446 Tota l 283

5 .47** 30 .26***

4 .39* 8 .54** 7 .35**

Z B i r thwe igh t was f i t t ed w i t h i n b reed and b i r th - type . :Separa te regressions o n b i r t h w e i g h t were f i t t ed for each b i r th - type . Levels of s ignif icance are ind ica ted by * (P< 0 .05 ), *(P< 0.01 ), * * * (P< 0 .001 ). EAT was d r o p p e d f rom t he mode l w h e n its e f fec ts were non-s igni f icant .

low rectal temperatures were associated with udder-seeking failure. None of the lambs which located the udder showed rectal temperatures below 35°C and there were few below 37~C, whereas the temperatures of those failing to find the udder covered a wide range down to 26°C. However, perhaps because of the tendency for a threshold effect, there was, over all breeds, no significant linear relationship between rectal temperature and the times taken to stand or reach the udder.

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DISCUSSION

This work revealed a wide range of variation in several aspects of neo- natal lamb behaviour. There were significant breed differences in time to stand for 3 min. There were also large and significant breed differences in udder-seeking performance, which probably reflected differences in the time taken to first suck, although, for technical reasons, this charac- teristic was recorded in only a few lambs.

Light lambs, because of their relatively large surface area to mass ratio, are susceptible to hypothermia (Alexander, 1974); some breeds are more suscep- tible than others (Sykes et al., 1976; Slee et al., 1980), and hypothermic lambs lack sucking drive {Alexander, 1964; Alexander and Williams, 1966a,b). Owens et al. (1979) found that single lambs stood and sucked quicker than the lighter multiples and survived better. These data suggested that light lambs might perform badly and that those breeds previously known to be liable to hypothermia might also perform badly. To some extent these predictions were justified. Within breeds, heavier lambs s tood more quickly and reached the udder faster than light lambs, irrespective of litter size. Between breeds, there was a general tendency for those with high average birthweights (Oxford and Border Leicester) to be slower to stand. However, the Finns, with lightweight lambs in large litters, performed poorly in all respects. Within breeds, lambs in multiple litters performed more slowly because of their lighter weights.

Since hypothermia may occur as early as 20 min after birth (Sykes et al., 1976), it was possible for early activity to have been slowed by hypothermia in some breeds where the average times required to stand for 3 min ranged from 17.5 to 54.0 min (Table IV). However, the later stages of behaviour involving udder-seeking were expected to be more seriously affected by adverse weather and by hypothermia. This was true overall in that weather conditions had a significant effect on the time to find the udder but not on the time to stand. Of those breeds with the lowest rectal temperatures (Finn, Merino, Southdown), only the Finns were deficient in early activity, but all three breeds showed consistently poor udder-seeking performance. Despite these relationships, a few hypothermic lambs with rectal tem- peratures between 35 and 37°C were able to find the udder successfully. Rectal temperatures did not necessarily reflect accurately the relative ability of all the breeds to resist hypothermia, because of the uneven distribution of breeds with respect to weather. However, other data (Sykes et al., 1976; Slee et al., 1980} showed that there were similar differences in resistance to hypothermia among the same breeds when they were exposed to more equal conditions, and that the most resistant breeds then were those with the highest rectal temperatures in the present experiments. Moreover, it was clear f rom the present observations that lambs with low rectal tem- peratures performed less well even if the causative roles of cold weather or innate susceptibility to hypothermia could not be separated in the present data.

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Slee et al. (1980) showed that the hill and feral breeds and the Oxfords tend to be resistant to cold in the field, and show better field survival rates, than the other breeds used. At the same time, the present data show the superiority of these same breeds for udder-seeking behaviour. The remaining four lowland breeds used in these experiments (Finn, Southdown, Merino, Border Leicester) rank low on all three criteria. The tentative conclusion is that udder-finding ability tends, with good resistance to hypothermia, to be associated with high survival ratings in the different breeds observed. Similarly, Owens et al. (1979) reported a relationship between the ability to stand and suck quickly after birth and subsequent survival in Booroola Merinos.

The breed differences found here suggest that udder-seeking and early sucking behaviour may be genetically influenced. This would not be un- expected, since under natural conditions successful sucking is a prerequisite for lamb survival, and there would be selection pressure in favour of efficient udder-finding. Early sucking might also be advantageous, before hypo- thermia began to inhibit the sucking drive and before the maternal bond began to weaken. The clearest findings in the present experiment were the deficiencies in udder-seeking and apparently in resistance to hypothermia in the Finns and Merinos. These breeds, particularly the Finns, are obviously unsuitable for lambing outdoors in cold climates such as that of Scotland.

ACKNOWLEDGEMENTS

We wish to thank M. Nicholl, S. Manson, R.G. Griffiths and S.B. Wilson for assistance in obtaining these observations.

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