Background last update:May 29, 2012

2013 approaches: What are the alternatives?

One more year and then all sows in the European Union ought to be housed in groups for most of their gestation phases. The transition to group housing systems is going differently in every European country. For those in doubt and for those interested: here's a recap of cause and effect, pros and cons, do's and don'ts.

Jeremy Bentham, the famous English philosopher and social reformer, was one of the first to address the issue of animal welfare by the end of the 18th century. He argued that the ability to suffer, not the ability to reason, should be the benchmark whether welfare ought to be applicable. For his time, he was a revolutionary thinker – nowadays he is often quoted by many animal welfarists around the world.
They may do so when referring to the fate of many sows around the globe, who spend their lives either in gestation crates or in farrowing crates. The European Union, in 2008, set out to put an end to this practice for its member states by launching a directive clearly stating what will be the rules for keeping gestating sows. In short, it meant that sows have to be kept in group housing during most of their gestation. Table 1 sums up all these requirements.Applying these regulations, a wide choice of novel housing systems appear. They depend on a variety of criteria and it depends on each individual pig producer which one to choose. Do the sows have to be fed individually or in a group? Is a restricted feeding regime or an ad libitum feeding regime preferred? Do the sows have to be physically separated during feeding? Should sows be fed simultaneously or sequentially? Do the sows have to live on straw? Does the producer want stable or dynamic groups?
Different preferences lead to different systems – they all have been extensively described. Some systems can be found in the illustrations below.
Critical issues
With these new system types, novel or hitherto unknown ailments and effects have come into view and it would be wise to touch briefly on every one of them.
Stress has been described as a biological response to an event that an individual perceives as a threat to its homeostasis. Scientists discern ‘acute stress’ and ‘chronic stress’. In the first case, it may affect fertility if it occurs at critical times. In the second, however, stress may have a more fundamental impact on fertility and metabolism of sows. In sows, stress factors lead to the production of corticosteroids in the pituitary gland – the hormone cortisol being the most well-known. These corticosteroids have a negative influence on the luteinic hormone (LH) and the follicle stimulating hormone (FSH), which eventually leads to lower amounts of progesterone and oestrogen being released. Cortisol is therefore known to be related to prevent oestrus and ovulation. In addition, cortisol is also known to lead to a delayed embryonic development around ovulation as well as at day 12-14 of gestation.
On the basis of these data, it would be logical to advise not to re-group the sows at 14 days into their gestation phase. Table 2 presents data from research on grouped sows by Kirkwood and Zanella, in 2005. It shows that the farrowing rate is smallest when the sows are re-grouped at 14 days.


Condition/ feed intake
A second critical issue is related to the sow’s condition due to feed intake. The regrouping in housing may lead to a temporal fasting as the sows need to adjust to the new housing situation. In early gestation, underfeeding may be present in submissive sows. Overfeeding can occur in dominant sows and can lead to more embryonic mortality in gilts. Similarly, the late gestation phase is not completely free of risks either, as there can be a loss of backfat in the last month, leading to more stillbirths.
Seasonal effects
Seasonal effects are known to play a strong role in group housing as well. In nature, hormonal changes make the LH production go down in sows, leading to a lower progesterone level and thus more repeat breeding and abortions. This effect is found in group housing as well. In combination with group housing, this could lead to extra risks.
Human-animal handling
Low reproductive performance can also be related to adverse animal handling, resulting in a fear for humans. Studies showed that gilts exposed to unpleasant handling, may show earlier puberty after being exposed to a boar.
Leg problems and longevity
A well-known critical issue that is related to group housing is that of leg problems. These could be caused e.g. by slippery floors, the poor quality of slats or bad hygiene. Bedding material may solve this problem, e.g. using straw on the floor. Apart from giving fewer injuries, they also offer physical and thermal comfort. Claw trimming has been suggested as a solution to the problem as well, but research by Ehlorsson and others (2004) showed that longevity is not improved by claw trimming.
Aggression among sows in group housing is a well-known phenomenon and it happens for two reasons. First is the competition for feed – this is usually short but frequent. In addition, there can be aggression in order to establish the social hierarchy with unfamiliar animals. This type of aggression is known to be particularly fierce. Strategies to deal with aggression can be found in managing the group size and its composition; being critical towards feeding systems, space allowance and hiding areas. In addition, the floor quality and straw provision can play a positive role.
Group housing & health
The housing system may offer effects on animal health hitherto unknown – and more research would be needed to evaluate these outcomes. First of all, stress can lead to a higher susceptibility for diseases. In addition, bacteria and viruses may possibly spread quicker, as there is more nose-to-nose contact, and more oral contact with faeces and urine. Hygiene and skin lesions may also be issues. On the positive side, animals in motion will lead to less constipation and less urine stasis.
A checklist for pig breeders can be found in the box. Whatever system producers decide to apply – the bottom line here is that it is not so much the system being the determinant, but rather a good management. This, in combination with a good welfare and health situation, is what makes group housing a success. Even Jeremy Bentham will then come to the conclusion that his words, about 180 years after his passing, finally had the desired effect in sow breeding. PP
This article is based on a paper presented at Ceva Santé Animale’s Trends in Sow Reproduction Symposium, Madrid, March 2011.
Group housing: Five do’s & don’ts
1 Introduction in group
• Gilts should become familiar with the feeding system (> 1 week)
• Gilts can be mixed with sows:
- introduction in subgroup for two-three days (e.g. mixing pen), allows fleeing behaviour (flight distance 10-12 m)
- housing first next to older sows, leads to sufficient social skills
- sufficient space
2 Space and group size
Large groups
- larger and more varied space
- no clear maximum (300)
- easier to include hide areas (visual barriers)
- less aggression, more avoidance
Small groups
- limited space, leading to stress
- more space needed per sow
3 Flooring and bedding
• Floors - non-damaging- e.g. not slippery, no damaged slats
• Bedding (when aggression is likely)
- reduces leg problems
- exploratory behaviour, less stereotypic behaviour
- lower risk for repeat breeding in early gestation
4 Group composition
• Keep consistent
•Sows have good social memory and recognise familiar animals following weaning
• Breeding gilts ought to be exposed to older dominant sows prior to introduction in large sow group
• Adding a mature boar in a group of sows leads to less aggression
5 Feed intake
• Sufficient feed intake during early gestation (submissive sows)
• Diets rich in fibre (ad lib):
- creating satiation
- promoting social stability
• Protection from aggression during feeding
• Individual feeding leading to homogenous body condition



By Prof Dominiek Maes, Unit Porcine Health Management, Department of Reproduction, Obstetrics and Herd Health, Ghent Uni

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