The Life History Of A Sow

Pigs have been domesticated for at least 5000 years but the European Scientific Veterinary Committee in 1997 made the important point that:

Although domestication and selection has altered basic aspects of the anatomy and physiology of the pigs, comparisons reveal that no major changes in basic behavioural systems have occurred during domestication.

As omnivores, foraging for food and exploration of their surroundings is an important part of the behaviour of both wild and domestic pigs. Even well-fed domestic pigs kept in a semi-natural enclosure are found to spend 6-8 hours a day searching for feed by rooting, grazing and browsing. Studies of wild and feral pigs show that they are naturally gregarious animals, the basic social unit being the maternal group of up to around six individuals. Similarly, domestic pigs form stable social hierarchies based on age and size. Pregnancy lasts about 115 days (just over 16weeks). Shortly before giving birth, both wild and domestic sows in natural surroundings choose a suitable nest site and build a nest of grass or soft materials. Free-range pigs stay in or close to the nest with the piglets for about 10 days, after which the piglets start to be integrated into the herd. In natural surroundings, weaning is completed at 13-17 weeks.

In commercial farming, young female pigs for breeding (gilts) are typically purchased at 5-6 months of age from specialist breeders, although they may also be reared on the farm. During rearing, they are usually kept in group housing. Gilts are usually served for the first time at their second or third oestrus after puberty, at 6-8 months of age. In some systems they are kept in group housing during their first pregnancy and then are moved to farrowing crates to give birth to their piglets.

Pregnant sows are moved from sow stalls to farrowing crates a few days before giving birth and the piglets are weaned and removed to indoor fattening units at 3-4 weeks of age in most European countries. Sows are typically served at the first post-weaning oestrus, which occurs 7-10 days after weaning.

A breeding sow in commercial production in Europe has on average 2.2 pregnancies per year and is expected to produce around 19-22 young pigs for slaughter every year. She may give birth to as many as 25 piglets a year, but at least 10% of piglets die between birth and slaughter. Around 40% of the sows in the average breeding herd are replaced per year. Typically a sow will produce 4-6 litters of piglets before being sent for slaughter at around 30-36 months of age because of reproductive failure or other health problems. An intensively kept breeding sow kept in a system using sow stalls is likely to spend three quarters of her life confined in a stall.

Welfare Problems Caused By Sow Stalls

It is generally accepted that confinement in stalls has detrimental effects on the welfare of sows both from the point of view of their physical health and equally their behavioural and psychological well-being. Well-managed alternative systems where the sows are not individually confined have a higher welfare potential in all these respects. Such alternatives include indoor group housing with straw and free-range housing outdoors where climate and soil are suitable. A survey of pig experts opinions published in the Netherlands Journal of Agricultural Science in 1999, put the stall and tether systems right at the bottom of their ranking of housing systems from the point of view of sow welfare.





The European Scientific Veterinary Committee’s Opinion

The most recent authoritative and official study of the effects of confinement in sow stalls on pregnant sows is in the European Scientific Veterinary Committee (SVC)’s 1997 report The Welfare of Intensively Kept Pigs. The report concludes unequivocally from the scientific evidence that sow stalls should not be used. It recommends that:

Since overall welfare appears to be better when sows are not confined throughout gestation, sows should preferably be kept in groups.

According to the report, when sows are in group housing rather that in stalls; the sows have more exercise, more control over their environment, and more opportunity for normal social interactions and better potential for the provision of opportunities to root or manipulate materials. As a consequence, group housed sows show less abnormality of bone and muscle development, much less abnormal behaviour, less likelihood of extreme physiological responses, less of the urinary tract infection associated with inactivity, and better cardiovascular fitness.

Further, the report states that sow stalls have “major disadvantages” for welfare:

The major disadvantages for sow welfare of housing them in stalls are indicated by high levels of stereotypies, of unresolved aggression and of inactivity associated with unresponsiveness, weaker bones and muscles and the clinical conditions mentioned above. Some serious welfare problems for sows persist even in the best stall-housing system.

The SVC states that it may be necessary to keep a sow temporarily in an individual pen within a group housing system, if she is sick or has been attacked. But their recommendation is:

No individual pen should be used that does not allow the sow to turn around easily.

Food Restriction and Confinement

Pregnant sows are normally fed restricted rations of concentrate feeds, to prevent them from putting on weight and to economise on concentrate feed costs. According to the SVC’s report;

The food provided for dry sows is usually much less than that which sows would choose to consume, so the animals are hungry throughout much of their lives.

Pigs in natural conditions spend much of their active time looking for food and eating it, whereas the commercial sow’s ration of concentrate feed can be eaten in a few minutes. The sow’s feed is sufficient for her bodily maintenance but does not necessarily satisfy appetite. This feeding regime has been described by a pig expert from the Scottish Agricultural College as being at odds with the sow’s feeding motivation. For confined sows kept in a barren cage without straw to chew and with no opportunity to go in search of food, food restriction must be made even more stressful. A number of studies of group-housed sows have shown that the provision of some bulky food or manipulable material such as straw reduces the welfare problems caused by feed restriction.

Feed restriction and confinement can also be related to gastrointestinal problems. In Denmark, where stalls and tethers are widely used, gastrointestinal problems have become a more common cause of death on intensive sow farms, according to a 1995 survey of sow mortality. They had risen to 20% of all causes of death compared to 5% in 1975. The most common life-threatening gastrointestinal disorder was gastric dilation (bloat), which results in painful ballooning of the stomach with gas. Gastric dilation often occurred when a confined sow suddenly got free access to feed because her neck tether was loose or the feed dispenser was damaged. There were few gastrointestinal problems in farms that provided straw bedding which the sows could use as roughage.
Health Problems Caused by Sow Stalls
The SVC’s report and numbers of other scientific studies have noted a wide range of health problems for sows that are either caused or made worse by confinement in sow stalls.





Inactivity, lameness and Injury

Lack of exercise adversely affects the bones and muscles of sows confined in stalls. A 1996 study from Cambridge University found that muscles used for walking were small in caged sows compared to the muscles of sows in group housing. In addition, lack of exercise also affects bone strength; the same team found that the bone strength of caged sows was only two thirds of the bone strength of group-housed sows. The scientists conclude:

The results indicate that confinement of sows, with a consequent lack of exercise, results in reduction of muscle weight and bone strength. Sows kept in stalls even have difficulty standing up and lying down. In an experiment at the Clinical Veterinary department at Cambridge University, they took over twice as long to lie down as group-housed sows. The major reason for this difference was the space restriction in stalls but the scientists suggest it is also caused by “the chronic effects of lack of exercise and the acute effect of floor type”. They conclude;

The results indicate that sows housed long-term in gestation stalls experience difficulty of movement when standing up quickly and lying down.

A German study in 1993 demonstrated how lack of exercise reduces sows’ physical strength and agility; 77% of sows confined during growth chose to lie down by leaning on a wall for support, compared to only 3% of sows loose-housed during growth.

When the sow stall is too small for the sow, the problems are even worse. A 1991 French study of the posture of sows suggested that the narrowest crates (0.60m) may make it difficult for sows to lie on their sides at all. A veterinarian told a 1998 conference of the German Veterinary Society that it was common to find large sows crammed into stalls measuring 1.8m long and 0.65m wide. The stall length was as much as 18 centimeters shorter than the body length of the largest sows and the width was too narrow to allow them to lie down on their sides with their legs stretched out. They had to lie with their heads in the feed trough. These stalls led to sows having difficulty in walking, grazed skin and even broken limbs.

Confined sows are also more likely to suffer from lameness. Evidence for this comes from several European countries. In 1996 a French study from INRA of nearly 1600 sows from 45 commercial herds found that lameness was more frequent in stalled or tethered sows. A 1995 study from Denmark (where 80% of sows were in stalls or tethered) found that leg weakness was the biggest single reason for the death or euthanasia of breeding sows (28%). The conditions included lameness, paralysis, arthritis and fractures. UK figures from the early 1900’s suggest that sows in stalls are 5 times more likely to be sent for slaughter because of lameness than sows kept outdoors.

One cause of lameness is the use of concrete or slatted floors in sow stalls. This type of flooring can result in chronic painful injury to confined sows. According to a leading Bristol University veterinary scientist, compared to outdoor sows;

Sows in stalls on concrete have a higher incidence of injuries to feet, inflammatory swellings of joints and abrasions to their skin. If these superficial abrasions become infected the infection may track down to damaged joints, set up septic arthritis and cause severe, chronic pain.

If the stall is too small or the bars badly adjusted, the result can be general bodily damage. Sows can be injured by the cage fittings. A 1997 French study of 692 sows from 16 farms found that sow stalls can interfere with movement and lead to physical deformity and skin injury. Nearly 27% of sows had deformation of the shoulder and 17% had inflammation or cysts on the skin of their front legs.




Urinary Tract Infections

Urinary tract infections are also more common in caged sows. The sows’ enforced inactivity is probably an important contributing factor. In France in the 1980’s scientists noticed that the incidence of urinary tract infections increased at the same time as sow stalls and tethers became popular in the pig industry. They also found that confined sows drink less than active sows, which could lead to concentrated urine and a greater chance for bacteria to multiply in the urinary tract. Infection can also be caused when confined sows have to lie on wet concrete in their own faeces.

Constipation is another effect of confinement in sow stalls, according to a 1997 publication by a German ethologist. This happens because the sows are unwilling to deposit their dung in the stall where they have to lie on it.




Cardiovascular Health

Lack of exercise also means that confined sows use their cardiovascular systems less. As a result, they are more prone to heart problems, which are a significant cause of death when pigs are transported. British veterinary scientists at Cambridge University studying heart-rate in pigs reported in 1993 that the level of cardiovascular fitness in stall-housed sows was less than the in group-housed sows. In 1997 they compared stall-housed pigs with pigs housed in a large group and in a small group. They found that the stall-housed pigs had a higher basal heart rate and a higher average heart rate when feeding than group-housed pigs, again indicating a lower level of bodily fitness for the confined pigs.





Reproductive Health

Breeding sows are sent for slaughter if they fail to become pregnant or have small litters. One possible cause for these problems is the sow’s housing conditions. According to the SVC, there is evidence that confined sows have more problems than group housed sows in coming into oestrus, that they take longer to give birth and that they have a higher incidence of mastitis/metritis/agalactia (MMA – a syndrome affecting sows after farrowing and involving inflammation of the udder and the uterus and lack of milk).





Stress and Immune System Function

Studies have found that confined sows have increased activity of the adrenal glands and higher concentrations of the steroid cortisol (hydrocortisone), associated with stress or activity. Stress is known to affect the immune system. Scientific results have indicated that sows who produce a greater cortisol response may also have a reduced immune response, which would make them less able to cope with infectious diseases.





Behavioural Problems Caused by Sow Stalls

Pigs are highly intelligent, inquisitive animals and there is abundant scientific evidence that they suffer when deprived of environmental stimulation and the opportunity to explore their surroundings.





How Sows Prefer to Live

There is considerable scientific evidence on sows’ preferences. From this it is clear that sows prefer not to be caged. According to the SVC Report, “In general, sows prefer not to be confined in a small space” and they “find the confinement aversive”. Sows show strong preferences for social companions and for rooting a bedding material. Considering the available research on sows’ preferences, the SVC concludes:

It is clear from such studies that sow welfare will be worse in conditions where exploration of a complex environment, rooting in a soft substratum and manipulation of materials such as straw are not possible, than in conditions where they are possible.

It has been known for many years that confinement prevents sows from carrying out important types of normal behaviour. Sows are social animals and have a need to establish a social hierarchy among themselves in order to avoid or resolve conflicts. As the SVC pointed out, this is usually impossible for sows in stalls. Ethological studies of sows carried out in Sweden in the 1980’s, when nearly two thousand social interactions between sows were observed, found that sows need to interact in order to resolve conflicts. The study concluded:

“Confinement (in stalls) decreased the social activity … and led to unsettled dominance relationships combined with high aggression levels…… The deconfinement system (loose housing) provided enough area for the sows to settle dominance relationships and to keep the aggression level fairly low”.

Sows in stalls are confined to one spot for all their activities, which is contrary to normal pig behaviour. Another early study from the Swedish Agricultural University showed that loose-housed sows chose to move between different areas of their housing for feeding, dunging and lying. They spent only 25% of their time in their feeding stalls, and then moved away. When given straw, the loose-housed sows used it for a variety of activities related to exploration, nest-building, predation and feeding whereas the sows confined in stalls could do nothing with the straw except eat it. These studies as long ago as the 1980’s showed that confinement in stalls frustrates basic behavioural needs of sows. Inevitably this frustration leads to abnormal behaviour.




Abnormal Behaviour

Common types of abnormal behaviour shown by confined sows are stereotypies, apathy, depression and lack of responsiveness. All of these are indicators that she is having difficulty coping with her environment and show that her welfare is not good.
Stereotypic behaviour is highly repetitive behaviour carried out for no apparent purpose. It includes bar-biting, chain-biting, sham-chewing (chewing air), pressing the drinker, nosing in the feed trough, tongue-rolling, head-weaving and attempts to root on the concrete floor. Stereotypies are very rare in sows kept in complex environments. Although they do occur among group-housed sows (especially when feed is restricted and no straw or similar material is provided), this is much less common than among confined sows. Unsurprisingly, sows spend more time on stereotypical behaviour when their food is restricted as well as their ability to move.

When sows are first confined they show no stereotypies immediately. The sows at first try to escape. They then appear to quieten down and may become inactive. Stereotypies only become frequent after several weeks of confinement, according to scientists in the Netherlands who studied the behaviour of confined sows in the 1980’s. Sows do not become well-adjusted to living in sow stalls. On the contrary, studies have found that the amount of stereotypical behaviour increases with the length of time the sow is confined over several pregnancies.

Stereotypies in confined sows have been reported from several European countries. A 1995 report from INRA/CNRS in France, for example, found that over 90% of stall-housed sows carried out apparently pointless tongue-rolling, bar and trough-biting, bar-licking and vacuum chewing. Another 1995 study from Cambridge University observed sows over four pregnancies. They found that by the fourth pregnancy stall-housed sows on average spent 14% of their time on activities that were clearly stereotypic and another 36% of their time on activities that were arguably stereotypic (such as rooting or chewing at pen fittings). In total, 50% of the sows’ time was spent on activities that were clearly or arguably stereotypic. The total average time spent on clearly stereotypic activity increased almost 12-fold between the first and the fourth pregnancy, showing that the problem got worse the longer the sows were confined. One particular sow spent over 40% of her whole time on clearly stereotypic activity, a sad comment on her welfare. Group-housed sows in contrast spent only on fifth as much time as the stall-housed sows, or less, on stereotypic activity.

The SVC Report points out that other studies may have missed stereotypies because they did not observe sows over a long enough period of time. The scientists conclude;

However, in every detailed study of sows in stalls or tethers, a substantial level of stereotypies has been reported indicating poor welfare in the sows.

Although the evidence is not yet entirely clear, scientists believe that stereotypies may have the function of reducing the level of stress hormone, cortisol, and that they may be associated with the release of endorphins (natural narcotics) in the sow’s brain as a way of coping with the stress of confinement.





Apathy and Depression

Abnormal inactivity and unresponsiveness are very widespread among confined sows. Studies have shown that sows in stalls are much less responsive than group-housed sows to any stimulus except food. Confined in a barren cage, their level of activity has been found to be very low – only about a quarter of that of sows with the opportunity to move and explore the environment.

The Scientific Veterinary Committee comments that since this inactivity and unresponsiveness is abnormal, it is likely that the sows are clinically depressed. Their behaviour is similar to depression in humans or to ‘learned helplessness’ which has been experimentally induced in animals.

The Need of Environmental Enrichment

In 1997 the Scientific Veterinary Committee considered environmental enrichment to be so important that they stated in paragraph 73 of their Conclusion and Recommendations;

All sows should have access to soil for rooting or manipulable material such as straw.

A 1994 study of sows’ preferences found that their demand for access to bedding materials was second only to their demand for food. Straw or other manipulable material is important for pig’s welfare in various ways; to provide a comfortable surface for walking and lying on, for thermal insulation, for rooting, for carrying and other manipulation and for chewing and eating. The fact that pregnant sows are feed restricted makes it more important for them to have access to these materials.

A number of studies in Germany, the UK and Switzerland have shown that providing sows with straw can reduce stereotypies and aggression at feeding time in all housing systems, especially when sows are feed-restricted. Straw can also be a useful feed supplement. Scientists in The Netherlands, Germany, Sweden, Norway and the UK have also reported improvements in the welfare of the sows when straw is used in group-housing systems. In the UK, studies have shown that an allowance of only 200g of straw per day each pig (used in the Straw-Flow system) resulted in fattening pigs spending nearly 30% of their time occupied with the straw and only a few percent of the time on negative interaction with other pigs. Experiments in Northern Ireland showed that sows benefit from being provided with recycled mushroom compost. The compost was not provided as bedding but was put in racks that the pigs could reach. The sows given compost were less likely to be aggressive and had very many fewer injuries than sows in a barren pen.





Alternatives to Sow Stalls

There are two types of housing system which are proven to be practical and successful alternative to the sow stall system.

1. Indoor housing of sows in groups (group-housing)
2. Outdoor breeding herds (free-range)

Even in countries where the stall system still predominates, it is now widely accepted that sow welfare is better in alternative systems. A 1999 survey of the opinions of eleven pig welfare experts from six European countries, who had all been involved in the development of housing systems for pigs, showed a “substantial degree of consensus” in their welfare rating of different housing systems for pregnant sows. They gave consistently the lowest welfare rating to the tether system and the stall system. Stalls and tethers “scored significantly lower” than indoor group housing systems and were “clearly ‘poor’ welfare systems”. The experts gave the highest welfare ratings to outdoor extensive systems and to the family pen system. The experts’ scores for the different systems were, from lowest to highest:

Tether, 1.8 points; sow stalls, 2.3 points; indoor group housing, 5.4-6.2 points; outdoor housing with huts, 8.0 points family pen, 9.1 points.

The ‘family pen’ is an experimental system for housing groups of 4-5 sows and gilts and their piglets together indoors. The pen includes nest areas with straw, activity areas, feeding areas and an outdoor yard. The piglets are reared in the family group up to slaughter weight. The system has been tested successfully on a commercial farm.