Gestation Stalls and the Welfare of Sows in Canada:

A Summary of the Scientific Literature

- February 2006 -

Summary ...................................................................................................................... 1

Introduction ............................................................................................................... 2

Productivity and Genetics Affecting Welfare ............................................................... 3

Space Limitations ......................................................................................................... 3

Physical Injuries and Ailments ..................................................................................... 4

Reduced Fitness ............................................................................................................ 4

Prevention of Natural Behaviours ................................................................................. 5

Stress ............................................................................................................................ 6

Aggression .................................................................................................................... 6

Public Pressure and International/ Global Trends .......................................................... 7

Conclusion ................................................................................................................... 8

References ..................................................................................................................... 9

Acknowledgement ..................................................................................................... 11

TABLE OF CONTENTS

Whittaker X, Edwards SA, Spoolder AM,Lawrence AB and Corning S. 1999. Effects ofstraw bedding and high fibre diets on the behav-iour of floor fed group-housed sows. AppliedAnimal Behaviour Science. 63:25-39.

Vieuille-Thomas C, Le Pape G and Signoret JP.1995. Steriotypies in pregnant sows: indications ofinfluence of the housing systems on the patternsexpressed by the animals. Applied AnimalBehaviour Science. 44:19-27.

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ACKNOWLEDGEMENTWorld Society for the Protection of Animals(WSPA) for generously funding the printing ofthis report.

To the average consumer, a pound of bacon looksmuch the same as it did 50 years ago. But the hogfarms that produce that bacon bear little resemblance to the small-scale, family operationsof yesteryear. Now, hog farms are large, intensivebusinesses holding thousands of pigs in conditionsthat might shock today’s consumers. One of themost controversial and disturbing developments ofmodern hog farming is the emergence of the sowstall.

Sow stalls are 1.2 square metres (approx.) metal-barred cages designed to keep labour costslow by isolating female pigs and thus reducing theneed to manage problems such as aggression andcompetition for food. They are also used toincrease sows’ pregnancy rates and litter sizes.Sows are kept in stalls for up to five years.

The extreme restriction of space prevents the sowsfrom engaging in even the most basic naturalbehaviours, such as rooting, or even turningaround. They are also denied more complexbehaviours such as building communal nests orforming social bonds – activities pigs naturallyengage in if given adequate space. The psychological effects of the confinement includestress, increased aggression and mental suffering.Evidence of stereotypies – repetitive movementsserving no function, such as bar biting – point tosuch suffering. As one scientist puts it, stereotypies can indicate the animal is “being driven insane.”

Worse still, the use of sow stalls leads to a range ofphysical injuries and ailments. These include jointdamage, urinary tract infections, lameness, boneweakness and muscle atrophy. Not surprisingly,the sows’ general fitness is diminished, indicatedby higher basal heart rates, less muscle and lowermobility compared to sows in freer environments.

These conditions, though demonstrably compromising the sows’ well being, are consideredacceptable under the Recommended codes of prac-tice, a set of voluntary standards for the keeping of farm animals in Canada. Despite theavailability of viable alternative (and morehumane) systems, Canada continues to use stalls.This contrasts sharply with policy in several otherplaces that have banned, or are planning to ban,sow stalls. In 2013, sow stalls will be bannedthroughout the entire European Union.

This report, reviewing available scientific literatureon the subject, sheds light on a practice that manyCanadians would find abhorrent. It makes astrong case for changing an inhumane system andfollowing the lead of other places toward morecompassionate treatment of pigs raised for food.

SUMMARY 1

The extreme restriction of space prevents

the sows from engaging in even the most

basic natural behaviours.

Gonyou H. 2005. Animal welfare – where we have

been and where we are going (presentation). 57th

Canadian Veterinary Medicine Conference. July,2005. Victoria, BC, Canada.

Jarvis S, Van der Vegt, Lawrence AB, McLean KA,Deans LA, Chirnside J and Calvert SK. 2001. Theeffect of parity and environmental restriction onbehavioural and physiological responses of pre-parturient pigs. Applied Animal BehaviourScience. 71:203-216.

Lawrence AB and Terlouw EMC.1993. A reviewof behavioural factors involved in the developmentand continued performance of stereotypic behav-iour in pigs. Journal of Animal Science. 71:2815-2825.

Manitoba Pork Council and Sask Pork. 2004.How pigs are raised. From website: www.saskpork.ca.

Marchant JN, Rudd AR and Broom DM. 1997.The effects of housing on heart rate of gestatingsows during specific behaviours. Applied AnimalBehaviour Science. 55:67-78.

Marchant JN and Broom DM. 1996. Factorsaffecting posture-changing in loose-housed andconfined gestating sows. Animal Science. 36:477-485.

Matthews LR and Ladewig J. 1994.Environmental requirements of pigs measured bybehavioural demand-functions. Animal Behaviour.43:713-719.

Mendl MT, Zanella AJ and Broom DM. 1992.The dexamethasone suppression test: an indicatorof depression and poor welfare in sows? Journal ofAnimal Science. 70:155

O’Brien T. 1997. The close confinement of Irishsows. Compassion in World Farming.

Petersen JS, Oksbjerg N, Jorgensen B, SorensenMT. 1998. Growth performance, carcass composi-

tion and leg weakness in pigs exposed to differentlevels of physical activity. Animal Science. 66:725-732.

Rolin BE. 1995. Farm Animal Welfare: social,bioethical, and research issues. Ames: Iowa StateUniversity Press. Pp75-78.

Schroder-Peterson D and Simonsen HB. 2001.Tail biting in pigs. The Veterinary Journal.162:196-210.

Spedding C. 2000. Animal welfare. Earthscan,London.

Stolba A and Wood-Gush DGM. 1989. Thebehaviour of pigs in a semi-natural environment.Animal Production. 48:419-425.

Turner SPG, Horgan GW and Edwards SA. 2001.Effect of social group size on aggressive behaviourbetween unacquainted domestic pigs. AppliedAnimal Behaviour Science. 74:203-215.

Terlouw EMC and Lawrence AB. 1993. Long-term effects of food allowance and housing ondevelopment of stereotypies in pigs. AppliedAnimal Behaviour Science. 38:103-126.

Terlouw EMC, Lawrence AB and Illius AW. 1991.Influences of feeding level and physical restrictionon development of stereotypies in sows. AnimalBehaviour. 42:981-991.

Weaver SA and Morris MC. 2004. Science, pigs,and politics: a New Zealand perspective on thephase out of sow stalls. Journal of Agriculture andEnvironmental Ethics. 17:51-66.

Webster J. 1995. Animal welfare: A cool eyetowards Eden. Blackwell, Oxford.

Whittemore CT. 1994. Causes and consequencesof change in the mature size of the domestic pig.Outlook on Agriculture. 23:55-59.

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Farming has changed dramatically in Canada overthe past 50 years. Historically, farms were self-suf-ficient and diverse, with small numbers of animalsrelative to land area. Animals spent most of theirtime intermingling with others while roaming andforaging for food. On modern farms, large num-bers of animals are contained within a small area(known as “intensive agriculture” or “factory farm-ing”), with greater productivity and efficiency tak-ing precedence over animal welfare. Due to thespecialization of farming practices, most farmsraise a single species. Hog farming, specifically, hasmoved from small farms of 50 free-roaming sowsto hundreds or thousands kept indoors in smallenclosures. For sows (female pigs), the majority oftheir adult lives are spent in sow stalls or gestationcrates (Manitoba Pork Council and Sask Pork,2004).

Sow stalls are concrete-floored, rectangular, metal-barred cages measuring on average 0.6 metres wideby 2.0 metres long (BC Ministry of Agriculture,Food and Fisheries, p.1), giving each sow approxi-mately 1.2 square metres of space. According tothe Recommended code of practice for the care andhandling of farm animals: Pigs, (Agriculture andAgri-Food Canada, 1993)

“[t]he length of a holding unit should allow acentrally positioned pig at least enough roomto move forward and backward, and liedown unhindered by a raised trough or reargate.”

This means that a sow should be able to stand up,sit or lie down and move a few steps forwards orbackwards. Approximately 75% of sows raised inCanada are raised in stalls (Manitoba Pork Counciland Sask Pork, 2004).

At around one year of age, sows are placed in stallsand kept there for between three and five years.They are artificially impregnated and remain inthese stalls until just before giving birth (parturition), when they are transferred to farrowing crates. Once the piglets are weaned, the

sow is re-impregnated and returned to the stall(Rollin, 1995). The purpose of sow stalls is toincrease the farming intensity, pregnancy rate andlitter size, while decreasing the human labour costsand to mitigate the problems associated with sowaggression (Weaver and Morris, 2004) and competition for feed (BC Ministry of Agriculture,Food and Fisheries, p.1). However, many animalwelfare groups and scientists have criticized sowstalls because they do not provide sows with:

• Adequate space to turn around or to perform many other natural behaviours observed in less restricted environments (Broom, Mendl and Zanella, 1995)

• Access to bedding, rooting or nesting material(Matthews and Ladewig, 1994)

In addition, sows in stalls typically displayincreased levels of:

• Chronic stress (Barnett et al., 1991)• Depression (Mendl, Zanella and Broom, 1992) • Frustration (Broom et al., 1995)• Urinary infections (O’Brien, 1997)• Sores from rubbing against metal bars (Anil et al,

2003)• Foot injuries (Anil et al, 2002; Marchant and

Broom, 1996)

Ironically, many of the studies cited to support theuse of sow stalls are also used to condemn them.Fraser (2003) suggests this may be a result of thedifferences in the motivation, philosophy and/orvalues of the researcher interpreting the studies.Duncan and Fraser (1997) also suggest differencesin approaches to studying animal welfare couldplay a factor.

The purpose of this report is to examine the useand applicability of sow stalls in Canada through areview of the current scientific and industry litera-ture. The focus of this paper is on animal welfareand excludes economic or political motivation.

INTRODUCTION 2

Agriculture and Agri-Food Canada. 1993.Recommended code of practice for the care andhandling of farm animals: Pigs. Publication1898/E.

Anil L, Bhend KMG, Baidoo SK, Morrison R andDeen J. 2003. Comparison of injuries in sowshoused in gestation stalls versus group pens withelectronic sow feeders. Journal of AmericanVeterinary Medical Association. Vol 223 No 9.pp1334-1338.

Anil L, Anil SS and Deen J. 2002. Evaluation ofthe relationship between injuries and size of gesta-tion stalls relative to size of sows. Journal ofAmerican Veterinary Medical Association. Vol 221No 6. pp834-836.

Barnett JL, Hemsworth PH, Cronin GM,Jongman EC and Hutson GD. 2001. A review ofthe welfare issues for sows and piglets in relation tohousing. Australian Journal of AgriculturalResearch. 52:1-28.

Barnett JL, Hemsworth PH, Cronin GM,Newman EA and McCallum TH. 1991. Effects ofdesign of individual cage-stalls on the behaviouraland physiological responses related to the welfareof pregnant pigs. Applied Animal BehaviourScience. 32:23-33.

Boyle LA, Leonard FC, PB Lynch, and Brophy P.2002. Effect of gestation housing on behaviourand skin lesions of sows in farrowing crates.Applied Animal Behaviour Science. 76:119-134.

BC Ministry of Agriculture, Food and Fisheries.Agriculture building systems handbook: Gestationpen stalls. Pp.1-4.

Broom DM, Mendl MT and Zanella AJ. 1995. Acomparison of welfare of sows in different housingconditions. Animal Science. 61:369-385.

Duncan IJH and Fraser D. 1997. Understandinganimal welfare. In: Appleby MC and Hughes BO(eds) Animal Welfare. pp 19-31. CABInternational: Wallingford, UK.

Fraser D. 2003. Assessing animal welfare at thefarm and group level: the interplay of science andvalues. Animal Welfare. 12:433-443.

Fredeen Ht, Sather AP. 1978. Joint damage in pigsreared under confinement. Canadian Journal ofAnimal Science. 58:759-773.

Giersing M and Andersson A. 1998. How doesformer acquaintance affect aggressive behaviour inrepeatedly mixed male and female pigs? AppliedAnimal Behaviour Science. 59:297-306.

REFERENCES 10

In 2013, stalls will bebanned for the entire

European Union.

â Stress induced bar biting is common in stalled sows. Photo courtesy of Compassion in World Farming.

PRODUCTIVITY & GENETICS AFFECTING WELFARE

SPACE LIMITATIONS

Due to the industrialization of farming, pigs, likeother intensively farmed animals, are bred formaximum production. Sows are specifically selected for maximum weight and back length(Whittemore, 1994). With these larger bodieshowever, the act of standing up or lying down hasconsequently become more difficult (Marchantand Broom, 1996). In stalls, where space is alreadylimited, larger body sizes cause an overall reduction in usable space, making it even moredifficult or, in some cases, impossible to move(Marchant and Broom, 1996). For sows, limitations on movement lead to stress (Barnett etal, 1991) and injury (Anil et al, 2003).

When an animal is selected for growth and productivity, secondary characteristics like behaviour are often compromised. Behaviourssuch as aggression or susceptibility to stress andfrustration are significant problems for sows installs. As these behaviours are partially determinedby genetics, selective breeding programs couldhelp mitigate some of these problems (Barnett etal, 1991).

Despite their reputation for being dirty and lazy,pigs are actually very clean and have a wide rangeof natural behaviours. Although they may spend alarge portion of their day resting, given unlimitedspace, pigs will forage, root, build nests and, if theyare farrowing sows, aggressively protect and takecare of their young (Stolba and Wood-Gush,1989). The location of their various activities willinclude sunny, shady, wet (marshy/muddy), dustyor grassy areas depending on the needs of the sow.They will have separate dunging and feeding areasas well. But on modern intensive farms, achievinghigh stocking densities and lower maintenancecosts have resulted in sows being housed in stallswith the minimum space required. Confined installs, sows are unable to perform many of theirnatural behaviours (Anil et al, 2002) and thereforeMarchant and Broom (1996) concluded that thecurrent system of sow stalling is inadequate.

Additionally, there are few laws in Canada govern-ing the size of stalls. The Recommended code ofpractice for the care and handling of farm animals:Pigs, the text used by the pork industry to set general husbandry standards, gives voluntary1

recommendations on stall floor space allowancesfor sows ranging in size from 100 to 250kg.

Unfortunately, not all sows fit into these guide-lines. Whittemore (1994) found that sow sizeshave been increasing to over 300kg. Gonyou(2005) pointed out that, as market prices fluctu-ate, so do the slaughter dates for a sow at the endof her typical four-year production period. Thismeans that some sows will be kept longer thanexpected and will grow larger than the stall wasintended to accommodate. As a result, her spacewill be even further restricted, and in some cases,she may protrude from the stall.

For sows in stalls, the limitation of space is one ofthe major causes of injuries observed in the porkindustry (Anil et al, 2003).

1In Manitoba, New Brunswick and PEI the stan-dards in the Recommended codes of practice aremandated by law, which may or may not beenforced.

3

Some sows will be kept longer than expected

and will grow larger than the stall was

intended to accommodate.

The scientific evidence is clear: sows suffer bothphysically and psychologically in stalls. The mostsignificant problems stem from a lack of space.With restricted movement, sows are unable tomove freely or perform natural functions such asforaging for food, rooting or nesting. As a result,fitness level decreases while physical injury, stress,occurrences of stereotypies and aggressionincrease.

The current system of stalling sows was developedmore than 50 years ago in response to a desire tosave money, time and space, as well as to meet societal needs and understanding of animal welfare

at the time. Humane standards and husbandry technology for raising pigs have changed dramatically since then, and better systems havebeen developed, both at home and abroad. Canadaneeds to follow the lead of other countries andphase out the use of sow stalls in favour of a morehumane system of raising sows. Canadian consumers must also accept their role in thischange, too. Consumers have a choice: they canchoose to support this outdated, inhumane system, or they can choose more compassionatesystems that provide sows with more a natural andmore humane environment.

9

Canada needs to follow the lead of other

countries and phase out sow stalls in

favour of more humane systems.

â Confined sows perform repetitive actions (stereotypies) as a result of boredom and stress. Photo courtesy of Global Action Network.

Two of the most convincing indicators of sowwell-being on farms are injuries and ailments (Anilet al, 2002). Physical injuries most often observedin confined sows include joint damage (Fredeenand Sather, 1978), external injuries (Anil et al,2002) and lameness (Marchant and Broom,1996). Ailments include decreased bone mass(Petersen et al, 1998) and urinary tract infections(Broom et al, 1995).

Because of their lack of movement, sows in stallstend to have weaker bone structures and greaterjoint damage in their legs than sows housed infreer environments (Weaver and Morris, 2004;Fredeen and Sather, 1978). When movement isrestricted, cartilage within joints tends to thicken,causing pain, which consequently makes move-ment more difficult and exacerbates the problem(Petersen et al, 1998). The result is even less move-ment and greater difficulty standing up or lower-ing their bodies.

External injures appear consistently on sows installs. Most stalls are too small to allow unrestrict-ed standing and lying down and have static designswhich do not adjust to the changing spatial needsof movement and growth (Anil et al, 2002;Marchant and Broom, 1996). As a sow’s sizeincreases, the time taken to stand up or lie downalso increases as a result of, among other reasons,the compounding spatial restrictions (Marchantand Broom, 1996). This means that sows are

forced to rub against the bars while raising or low-ering their bodies (Anil et al 2003). In some cases,because of inadequate stall width, larger sows haveto put their limbs into adjacent stalls when lyingdown and are subsequently injured by beingstepped on (Anil et al, 2002). Such injuries tend tobe observed less in sows housed in outdoor systemswith larger amounts of space (Barnett et al, 2001).

The muscles of sows in stalls are affected by thelack of movement (Marchant and Broom, 1996).As with most mammals, lack of use causes muscleatrophy and reduced strength. This, combinedwith joint damage and weaker bones, leads to sec-ondary injuries that result from sows slippingbecause of a lack of control standing up orsitting/lying down (Boyle et al, 2002; Marchantand Broom, 1996). These injuries can includeabrasions, damaged ligaments, broken bones andbruising.

Flooring in stalls is usually slatted, partially slattedor solid bedded. Marchant and Broom (1996)concluded that these types of flooring might causelameness in confined sows. O’Brien (1997) alsoblamed these types of flooring for the increase inurino-genital infections observed in stalled sows.Marchant and Broom (1996) concluded, however,that using a less slippery, warmer and drier floor-ing substrate such as straw could easily rectify suchflooring problems.

PHYSICAL INJURIES & AILMENTS

REDUCED FITNESS

4

Maintaining fitness in any animal requires move-ment. But for sows in stalls, movement is severelylimited. The result is decreased muscular tissueand lower cardiovascular strength (Marchant andBroom,1996).

To quantify fitness, basal heart rate, mobility andmuscle development are often measured. For basalheart rate, a lower rate typically implies better fit-ness. Sows in stalls, however, tend to have higher

basal heart rates compared to sows in freer envi-ronments (Marchant et al, 1997). For mobilitymeasurements, the ease and ability to stand up orlie down are usually measured. Sows in stalls typi-cally take significantly longer to perform thesetasks compared to group-housed sows (Marchantand Broom, 1996). Muscle development is physi-cally examined and sows in stalls tend to have lessmuscle, particularly in third and fourth pregnan-cies (Broom at al, 1995). Interestingly, Marchant

Additionally, in 1991, Bure found most aggressionin sows occurred as a result of sows feeling unsatisfied because of restricted access to feed or alack of satisfaction of feeding motivation(Whittaker et at, 1999). Anil et al (2003) hypothesized that increased appetite is a majorcause for aggression in sows.

8

Sows in stalls generally find theirconditions more aversive than

any other housing system.

Whether sows should be raised in stalls or not isboth a scientific and an ethical question (Weaverand Morris, 2004) and therefore interpretingbehavioural and physiological measures in terms ofanimal welfare is extremely controversial. Thereare great discrepancies over the relative importanceof different measures (Broom et al, 1995). For thisreason, Broom et al (1995) suggest that any onemeasure on its own should provide evidence that

welfare is poor (Broom et al, 1995).

“While it is not always obvious what causes painin animals, common sense and the argument fromanalogy would suggest that, unless it can be provedotherwise, anything that is physically painful forhumans must be assumed to be painful to animals”(Weaver and Morris, 2004).

CONCLUSION

In recent years, the public has been demandingassurance that animals on farms are treatedhumanely (Anil et al, 2003). Sow stalls do notmeet this demand and many places have bannedthe use of sow stalls in favour of other, less confining systems such as group housing. Sweden,the United Kingdom and Denmark have alreadybanned stalls. Finland will ban stalls in 2006. TheNetherlands and the state of Florida (USA) havebans that will come into place in 2008. In 2013,stalls will be banned throughout the entireEuropean Union.

To assume that simply changing the method ofhousing will solve all the welfare problems is incorrect. Although Broom et al (1995) foundthere were more welfare problems for sows housedin stalls than in group housing, they cautioned: forgroup housing to be effective, sows need a space of5m by 2.2m or larger. Gonyou (2005) suggestedthat choosing a feeding system that was both suitable to the pigs and easy to understand and

operate by the producer was also critically important. Any method of housing requires modification to make it more humane and caremust be taken to ensure that changes in housingsystems do not improve some aspects of welfarewhile making others worse (Anil et al, 2003).

But viable alternatives to sow stalls are alreadyavailable in Canada. In an interview in theFebruary 3rd 2005 edition of the Western Producer,Peter Brooks of the University of Plymouth said:

“There’s no doubt about it: we have gotsystems which are every bit as good, ascheap to operate, as easy to operate, ascheap to build, as sow stalls.”

As have people in other countries, Canadians mustdecide what housing system is acceptable.

PUBLIC PRESSURE & INTERNATIONAL/GLOBAL TRENDS

5

â Sows are kept in stalls for 3 to 5 years. Photo courtesy of Global Action Network.

Animals under humancare should not be subject-ed to environments wheresuch coping mechanisms

[stereotypies] are required.

and Broom (1996) found that group-housed sowshad significantly longer bodies than stalled sowseven though they came from the same geneticstock. This indicates that exercise affects thegrowth and development of bone and muscle.

Using basal heart rate, mobility and muscle development as a measurement for fitness, sows installs are generally viewed as having lower physicalfitness than sows in other housing systems(Marchant et al, 1997).

PREVENTION OF NATURAL BEHAVIOURSWhen domestic pigs are given sufficient space orraised in wild environments, they behave almostidentically to wild pigs (Stolba and Wood-Gush,1989). This includes having separate dunging andfeeding areas, spending significant amounts oftime rooting, building communal nests and form-ing complex social bonds. Sows in stalls are prevented from engaging in these behaviours and,like most animals placed in barren environments,show repetitive and destructive behaviours instead(Weaver and Morris, 2004). These include stereo-typies, which are repetitive movements that serveno function other than filling time and are an indication of mental suffering (Webster, 1995;Spedding, 2000). They can also mean an animal isbeing driven insane (Spedding, 2000). Like mostanimals kept in captivity, sows in stalls show distinct stereotypic behaviour (Lawrence andTerlouw, 1993).

Broom et al (1995) found that stall-housed sowsdeveloped more stereotypies than group-housedsows. The stereotypies tended to be oral movements, with bar biting being the most com-mon (Vieuille-Thomas et al, 1995). Chewing onbars is a sign of a lack of oral satisfaction(Lawrence and Terlouw, 1993), but it can alsoreflect a lack of environmental stimulation(Whittaker et al, 1998) or inappropriate housingsince, unlike other stereotypies, bar biting is notreduced by the addition of straw (Vieuille-Thomaset al, 1995).

The long-term confinement of sows has also led tosome modification of the animals’ posture-changing behaviours, as a result of being unable toexercise (Marchant and Broom, 1996). For exam-ple, while raising or lowering her body, a sow mayinterrupt the action several times before completing the task.

Another stressor for pigs is the restriction on theirability to stay clean. Despite their association withmud and general uncleanliness, pigs are extremelyclean. They even have separate dunging, eatingand sleeping areas. One of the signs of discomfort

is “dunging and eating in sleeping areas”(Agriculture and Agri-Food Canada, 1993). Installs, pigs are forced to dung, sleep and eat all inthe same area, and this in itself causes some level ofstress.

Being social animals, pigs display varying levels ofaggression depending on their environment.Schroder-Peterson and Simonson (2001) concluded that some of the causes for aggressioninclude overcrowding, lack of straw or other bedding materials, lack of environmental enrich-ment, inappropriate temperatures, inadequateventilation, hunger, poor nutrition and stress.

Sows in stalls live in confining, barren environments lacking environmental enrichment.It should come as no surprise then that overt andantagonistic aggression is higher in stalls than infreer systems, with aggression tending to escalatebecause sows can’t use active avoidance strategies(Broom et al, 1995). When space is reduced, incidences of aggression between neighbouringstall-mates cause injuries (Anil et al, 2002) andstress (Broom et al, 1995).

Sows in stalls generally find their conditions moreaversive than any other housing system (Broom etal, 1995). As a result, aggression tends to be less ofa problem in outdoor-housed sows with largeamounts of space (Barnett et al, 2001). However,because sows are not well adapted to interruptionsin social hierarchy or the introduction of strangersto a group (Giersing and Andersson, 1998), themixing of unfamiliar pigs into groups can causeaggression (Turner et al, 2001). This is easily rectified, however, by introducing small groups ofpigs into larger groups at a young age, or by providing large areas for escape for less dominantpigs (Turner et al, 2001). Interestingly, whenreturning from farrowing crates, sows in groupsshowed lower levels of overt aggression than thosein stalls (Broom et al, 1995). This may be a resultof becoming accustomed to other pigs during theirpre-farrowing period.

AGGRESSION

7

Sows in stalls live in confining, barren

environments lackingenvironmental

enrichment.

â Stalls are concrete-floored, metal-barred cages. Photo courtesy of Global Action Network.

Most sows in Canada are on food-restricted dietsto prevent excessive weight gain and to maintainlower production costs, yet food restriction may beone of the most significant factors in the development of stereotypies (Terlouw et al, 1991).But it is not the only factor. Stolba and Wood-Gush (1989) found no evidence of stereotypies infood-restricted sows in semi-natural environments,leaving Terlouw and Lawrence (1993) to concludethat food restriction does not function independently of housing condition. The development of stereotypies, therefore, is often theresult of a complex interaction among food deprivation, food ingestion and housing (Terlouwand Lawrence, 1993).

Sows have a strong instinct to nest before giving

birth and will work very hard to access appropriatebedding material (Mathews and Ladewig, 1994).In stalls, however, sows are unable to build nests,which inevitably leads to stress and frustration andmay be a further cause of stereotypies.Correspondingly, group-housed sows have significantly lower incidences of stereotypies thansows in stalls (Vieuille-Thomas et al, 1995).

In their paper titled Science, pigs, and politics: aNew Zealand perspective on the phase-out of sowstalls, Weaver and Morris (2004) wrote:

“Animals under human care should not besubjected to environments where suchcoping mechanisms [stereotypies] arerequired.”

Measuring stress can be difficult since the stresshormone cortisol is released for both physical painand excitement (Fisher, 1998). Yet even with theselimitations, Barnett et al. (1991) concluded thatstalls cause sows chronic stress, and Jarvis et al(2001) concluded the inability to nest while installs causes acute stress. Like all animals, pigs feel

stress when placed in conditions that are new, limiting or contain unfamiliar sounds, smells orobjects. For sows in stalls, space and food limitations, the inability to turn around and theinability to nest are often viewed as the most common causes of stress.

STRESS

6

â Sows are only able to move a few steps forward or backward. Photo courtesy of Global Action Network.

Space and food limitations, the

inability to turn aroundand the inability to nestare often viewed as themost common causes

of stress.