Effects of two mixing times post-service on the welfare of sows in a group housing system with free access stalls

Abstract

European legislation (2008/120/EC) allows sows to be kept in gestation stalls for up to 4 weeks after service, but there are increased societal calls to reduce and/or ban their use. Mixing sows is inevitably associated with aggression, while reducing time spent in stalls means mixing sows into groups earlier after service. There is little research on the magnitude of the associated effects on sow welfare in different group housing systems. The aim of this study was to determine the effects of mixing sows (6 groups/treatment, 12 sows/group) in pens with individual free access feeding stalls two days (2D) or four weeks (28D) after service on aggressive behaviours and skin lesions up to the first three weeks post-mixing, on locomotory ability 8 weeks post-mixing and in late pregnancy and on reproductive performance and litter size. Direct observations of aggression (all-occurrence sampling, 2 hrs/day) were conducted immediately after mixing (T0), 24hr (T1), 8 days (T8) and 3 weeks post-mixing (T21). Skin lesions were counted at T1, T8 and T21. Sows were locomotion scored using a visual analogue scale. An effect of treatment was observed only on the number of fights recorded at T1, which was higher in 2D sows. Furthermore, numbers of fresh skin lesions remained high in both treatments 8 days post-mixing. This could reflect a prolonged dominance hierarchy establishment because of sows ‘hiding’ in the free-access stalls. Taken together these findings may explain numerically lower pregnancy and farrowing rates in sows mixed two days post-service in spite of few other serious implications of this mixing treatment for sow welfare.