Pigs establish stable dominance hierarchies that reduce aggression within groups. Disrupting these social structures through regrouping causes significant welfare costs in commercial pig farming systems.
Pig social behaviour creates a welfare paradox: pigs thrive in stable groups but commercial management requires frequent regrouping that triggers repeated aggression cycles. Each regrouping event causes acute suffering through fighting, with injuries to ears, tails, and flanks. The cumulative welfare burden of multiple regroupings across a production cycle is substantial. Management strategies that minimise regrouping frequency, provide adequate space and enrichment to diffuse aggression, and phase introductions rather than abrupt mixing reduce but cannot eliminate this welfare cost. Stable group management from weaning through slaughter where commercially feasible is the welfare-optimal approach.