10 November 2023

Elevating gestating sow welfare – a win-win for sow and piglet performance

Laura Boyle and Keelin O’Driscoll tell us that since the 2013 ban on individual housing for pregnant sows after 28 days of pregnancy was introduced, the focus on pig welfare in the EU switched to implementing the ban on tail docking.

Most producers concede that they would never go back to individual housing and getting sows out of stalls undoubtedly led to many welfare improvements. However, our group housing systems are far from perfect and they still present numerous challenges for sows relating to aspects of the physical and social environment.

For example, sows are kept at relatively small space allowances on slatted floors where they are exposed to aggression at mixing and often at feeding. As a result, they suffer from fear, skin lesions, injury and lameness associated with pain and acute/chronic stress. In spite of this, most sows perform remarkably well reproductively in Irish systems of group housing. Nevertheless, increasing sow mortality and replacement (currently 60% in Ireland as per Interpig, 2022) rates, as well as the poor state of cull sows at slaughter is the main evidence of the toll the system takes on these animals.

Chronic stress in pregnant sows exposes their piglets to stress hormones in utero, mainly cortisol. This ‘pre-natal stress’ has negative effects on pigs’ ability to cope with stress in life and also has a detrimental impact on their immune function and resilience to disease.

Large litter sizes exacerbates these effects. Not only are piglets born smaller and more vulnerable, but they are also more crowded in the farrowing house in the weeks prior to weaning. The need to raise pigs without medications and increasing societal expectations for high standards of welfare in pig production warrants a renewed focus on sow welfare during pregnancy.

The SowWeanWel project aimed to wean resilient and healthy pigs from sows that experienced better welfare during pregnancy. During the project, we collaborated with researchers in the University of Padua in Italy, who also had a renewed interest in the welfare of sows during pregnancy, particularly early pregnancy.

Current EU legislation permits the keeping of sows in stalls during this period. This partnership was timely, as it coincided with the European Food Safety Authority’s (EFSA) plans to revise the Scientific Opinion on Pig Welfare with particular focus on the welfare of sows during the first 28 days of pregnancy. This report was published in 2022 and underpinned an EU commitment to phase out and eventually prohibit the use of cages for farm animals by 2027. In recent weeks, there are signs that the EU may reverse this commitment because of fears of higher food prices when consumers are experiencing a cost of living crisis.

Detrimental effects of aggression on reproductive performance

Aggression and the associated fear and injury, mainly in the form of skin lesions but also lameness, are among the main welfare problems for sows housed in groups on commercial farms.

We are all aware of the detrimental effects of aggression at mixing, but we rarely consider the impact of prolonged aggression. In the first study (performed on a commercial farm in Ireland), we counted skin lesions on sows one day (acute stress indicator) and three weeks (chronic stress indicator) post-mixing (after 28 days spent in stalls post service) into a fully slatted group housing system with free-access stalls.

Counts of skin lesions three weeks post-mixing were associated with both the number of mummified piglets, and Intra Uterine Growth Retardation (IUGR) scores – indicating that when sows experienced chronic aggression, they delivered more mummified piglets and piglets were less developed at birth.

In another study on the same farm, we provided six groups of 20 sows with straw in three racks in the loose area and with ropes in each of the free-access stalls (Improved). We compared them with another six groups that had only one chain and a piece of wood between the 20 sows in the group (Control). We found less aggression overall in the improved groups – particularly 21 days post-mixing – this is important as this was the time when we found the association between skin lesions caused by aggression and poorer reproductive performance in the previous study. Therefore, improving the quality of environmental enrichment provided to sows reduced aggression in the long term.

The high-quality enrichment had little effect on the amount of fighting by sows at mixing – this is not surprising. Sows have to fight at mixing to form a dominance hierarchy (DH). This is evolutionarily very important to group stability, so it is very difficult to distract sows from fighting at mixing.

Stage of mixing

Aggression at mixing is inevitable, but as outlined in the Pig Welfare Scientific Opinion, (EFSA, 2022) we can mitigate the consequences by giving sows enough space, places to hide and by mixing them on solid flooring.

Certainly, group-housing systems with free-access stalls provide a place for sows to escape to and hide from aggressors at mixing, but it raises the question as to how long it takes to establish the DH in such systems. Some sows may ‘hide’ in the stalls and thereby take longer to secure their place in the ‘pecking order’.

We believe this might explain why sows mixed into this group housing system two days post-service had a numerically lower pregnancy (83%) and farrowing (80%) rates compared to sows mixed into the same system 28 days post-service (94 and 88% respectively).

Normally the DH settles 24 to 48 hours post-mixing but in this housing system, we found relatively high counts of fresh skin lesions in both treatments eight days after mixing indicating ongoing fighting. For sows mixed two days post-service, this was getting close to the period of implantation where stress arising from aggression is detrimental to the success of the pregnancy.

Numbers of sows (144) on the trial were low but this trend merits further investigation for this housing system if the EU prohibits keeping sows in stalls for 28 days post-service. One solution would be to close the stalls off from the sows when they are introduced to the pen to ensure rapid establishment of the DH, but this would likely result in severe aggression (and therefore stress, injury and lameness) in the first 24 hours.

In a similar study conducted on an Italian farm where sows were mixed into pens (floor feeding/100% solid concrete/no free access stalls) of 21 sows four or 28 days post-service, there were no effects of day of mixing on sow welfare or reproductive performance (pregnancy rate: 85% at four days and 88% at 28 days; farrowing rate: 81% at four days and 84% at 28 days). This is consistent with conclusions reached by the expert panel working with EFSA on the Scientific Opinion on Pig Welfare that stage of pregnancy at mixing has little impact on sow reproductive performance (EFSA, 2022).

Better sow welfare has consequences for pre-natal stress

We already showed how providing sows with good environmental enrichment reduces aggression in group housing systems (although sows are possessive of the straw and sometimes threaten other sows trying to access it). Rubber mats in the free access stalls also conferred comfort benefits to sows in the improved environment.

Unsurprisingly then we saw a general reduction in indicators of chronic stress including less stereotypies, lower tearstain scores and lower levels of inflammatory markers. As predicted under the pre-natal stress hypothesis, these welfare benefits to the sows conferred advantages to their piglets. Sows who were in improved pens during pregnancy gave birth to fewer mummified piglets, and their piglets had fewer indications of IUGR. More importantly, piglets born to sows from improved pens had less diarrhoea during the suckling period (farrowing pens were scored for dirtiness, i.e. scour, on a weekly basis from birth to weaning).

At Moorepark, we worked in detail with pregnant gilts having intrinsically different health and stress profiles (manifested in different locomotory abilities, levels of sham chewing/stereotypies, patterns of ESF use and skin lesion scores). We found that their piglets differed accordingly in terms of the severity of IUGR and in their reactivity to stress. It is also worth mentioning briefly that even though none of these gilts were ever clinically lame during pregnancy even slightly impaired locomotion in early pregnancy was associated with higher levels of cortisol and more piglets born dead. This emphasises yet again the underappreciated impact that lameness has on welfare, performance and therefore farm profitability.

How to detect lameness

Locomotion scoring is the best way to detect lameness early. For gilts in particular, this could save them from exiting the herd before earning a return on investment. Detecting subtle changes in a gilt’s walking ability requires a sensitive method so we developed a ‘visual analogue scale’ scoring system (available on the Teagasc website).

Take home points

Chronic aggression in sows has detrimental effects on reproductive performance.
Providing sows with good enrichment and comfort during pregnancy not only reduces aggression, but also improves welfare in general and reduces chronic stress.
In most group housing systems, there are few differences in welfare or reproductive performance of mixing sows two versus 28 days post-service.
There are indications that mixing sows two days post-service into group housing systems with free-access stalls could interfere with reproductive performance.
Improving sow welfare has important advantages for piglet health and resilience at birth, during the suckling period and likely throughout its life.
Locomotion scoring is crucial for the early detection and treatment of lameness references available on request.