Mixing pigs from different social groups causes severe aggression and welfare harm, and management strategies maintaining stable groups from weaning to slaughter significantly improve outcomes.
Social group stability is a fundamental welfare determinant for pigs. Unlike the individualized housing that characterizes some intensive systems, pigs are social animals that establish and maintain dominance hierarchies through experience with known individuals. When unfamiliar animals are mixed, the resulting fights to re-establish hierarchy cause genuine suffering — physical injury, stress, and disrupted sleep and feeding for days following mixing. The welfare solution is not complex in principle: maintain stable social groups from birth through to slaughter. Implementation requires production system design that eliminates regrouping events at weaning, pen moves, and pre-slaughter staging. Systems that have achieved this through facility redesign show substantially better welfare outcomes across the production cycle.