Breeding sows better suited to group housing

The re-introduction of group housing for gestating sows in Australia, and elsewhere, has implications for both sow welfare and performance through enabling interactions (both positive and negative) between sows. Several strategies were investigated to identify selection criteria which might facilitate selection of sows better suited to group housing. These include: 1) estimation of social genetic effects; 2) use of proximity loggers for recording contacts between animals in groups; and 3) evaluation of flight time and fight lesion scores as potential selection criteria. Using strategy 1, significant social genetic effects were evident for litter size outcomes of group-housed sows. This implies that interactions between sows in groups have an impact on their reproductive performance, and this could be accommodated by appropriate models to estimate breeding values simultaneously for social genetic and additive genetic effects. Using strategy 2, proximity loggers provided opportunities to record all contacts between individual sows in group settings, but on animal implementation with off-the-shelf collars and modified (with harness) loggers failed in the age class of interest (gilts). Using strategy 3, both flight time and fight lesion scores were moderately heritable, but only fight lesion scores recorded 24 hours post-mixing in gilts had any association with other important sow characteristics. Preliminary parameter estimates suggest that under current housing and selection in maternal lines, post-mixing fight lesions recorded gilts would be expected to reduce, favouring improvement in some welfare related traits. Additional direct selection against fighting behaviour is also possible, and would be expected to reduce early culling of gilts. Overall, while developing meaningful selection criteria based on behavioural attributes which are practical to implement in commercial breeding programs is difficult, some opportunities to improve sow welfare and performance in group housing were identified in our studies.