Individual variation in sow aggressive behavior and its relationship with sow welfare

This study examined the relationships between individual sow aggressive behavior and sow welfare, based on aggression, skin injuries, and stress, in a total of 275 pregnant domestic sows. Over 4 time replicates, sows were randomly mixed into groups of 10 (floor space of 1.8 m²/sow) within 7 d of insemination in both their first and second gestations (200 sows per gestation with 126 sows observed in both gestations). Measurements were taken on aggression (both delivered and received) at feeding, skin injuries, and plasma cortisol concentrations at d 2, 9, and 51 after mixing. Live weight gain, nonreproductive removals, litter size (born alive, total born, and stillborn piglets), and farrowing rate were also recorded. In both the first and the second gestations, sows were classified at d 2 after mixing as “submissive” (delivered little or no aggression at feeding relative to aggression received), “subdominant” (received more aggression at feeding than delivered), and “dominant” (delivered more aggression at feeding than received). In both gestations, sows classified as dominant at d 2 subsequently delivered more (gestation 1, P < 0.01; gestation 2, P < 0.01) and received less (gestation 1, P < 0.01; gestation 2, P < 0.01) aggression and gained the most weight (gestation 1, P < 0.01; gestation 2, P < 0.01). Dominant sows had the least skin injuries throughout gestation 1 (P = 0.04), and although submissive sows sustained the most skin injuries at d 9 and 51 of gestation 2, at d 2 the classifications did not differ in skin injuries (P < 0.01). Subdominant sows had the highest cortisol concentrations at d 2 of gestation 2, but there were no differences between classifications at d 9 and 51 in either gestation (gestation 1, P > 0.05; gestation 2, P = 0.02). There were no significant relationships between aggression classification and reproduction and nonreproductive removals (P > 0.05). In conclusion, sows classified as dominant at feeding at d 2 subsequently received less aggression at feeding, sustained fewer skin injuries, and had higher live weight gain. Submissive and subdominant sows in groups are likely to benefit from the provision of increased resources such as space and access to feed.