Social status and previous experience in the group as predictors of welfare of sows housed in large semi-static groups

Citation

Brajon, S., Ahloy-Dallaire, J., Devillers, N., Guay, F. (2021). Social status and previous experience in the group as predictors of welfare of sows housed in large semi-static groups. PLoS ONE, [online] 16(6 June), http://dx.doi.org/10.1371/journal.pone.0244704

Plain language summary

Mixing gestating sows implies hierarchy formation and has detrimental consequences on welfare. The effects of social stress on the most vulnerable individuals may be underestimated and it is therefore important to evaluate welfare between individuals within groups. This study aimed at investigating the impact of social status and previous experience in the group on well-being of sows housed in large semi-static groups. We assessed aggression, body lesions and feeding order on 20 groups of 46–91 animals. Social status was based on the proportion of fights won and sows were categorized as Dominants (29%), Subdominants (25%), Losers (23%) and Avoiders (23%). Some sows (70%) were already present in the group in the previous gestation. The welfare of sows differed between individuals within the social groups according to their social status, based on the fight winning, and their previous experience in the group (i.e., whether they were already resident in the group in the previous gestation or new). Subordinate sows are more likely to avoid aggressive individuals when mixed in large pens with higher group size. However, they suffered from more body lesions than higher-ranking sows later during gestation. Sows newly introduced into the groups paid the cost of being new since they were more involved in agonistic interactions and maintained higher body lesions scores. Many questions remain open and future studies may thus investigate more deeply the social relationships of sows housed in large groups, including the extent to which pigs can develop preferred affiliative relationships with specific partners.

Abstract

Mixing gestating sows implies hierarchy formation and has detrimental consequences on welfare. The effects of social stress on the most vulnerable individuals may be underestimated and it is therefore important to evaluate welfare between individuals within groups. This study aimed at investigating the impact of social status and previous experience in the group on well-being of sows housed in large semi-static groups. We assessed aggression (d0 (mixing), d2, d27, d29), body lesions (d1, d26, d84) and feeding order on 20 groups of 46-91 animals. Social status was based on the proportion of fights won during a 6-hr observation period between d0 and d2. Dominants (29%) were those who won more fights than they lost, Subdominants (25%) won fewer fights than they lost, Losers (23%) never won any fight in which they were involved while Avoiders (23%) were never involved in fights. Resident sows (70%) were already present in the group in the previous gestation while New sows (30%) were newly introduced at mixing. Subdominants and Dominants were highly involved in fights around mixing but this was more detrimental for Subdominants than Dominants, Losers and Avoiders since they had the highest body lesion scores at mixing. Avoiders received less non-reciprocal agonistic acts than Losers on d2 (P = 0.0001) and had the lowest body lesion scores after mixing. However, Avoiders and Losers were more at risk in the long-term since they had the highest body lesions scores at d26 and d84. They were followed by Subdominants and then Dominants. New sows fought more (P<0.0001), tended to be involved in longer fights (P = 0.075) around mixing and had more body lesions throughout gestation than Resident sows. Feeding order from one-month post-mixing was influenced both by the previous experience in the group and social status (P<0.0001). New sows, especially with a low social status, are more vulnerable throughout gestation and could serve as indicators of non-optimal conditions.

Publication date

2021-06-01

Author profiles