Understanding pig social behaviour is essential for managing group-housed pigs in ways that minimise aggression and support positive social welfare states.
Pigs are highly social animals with complex dominance hierarchies that, once established, produce relatively stable groups with manageable levels of social conflict. The welfare problem arises at mixing events — when unfamiliar pigs are combined, which occurs repeatedly across commercial production at weaning, nursery transfer, and gestation grouping. Mixing triggers serious aggression as pigs establish new hierarchies, with injury rates and stress responses that represent acute welfare harm. Management strategies that minimise mixing events, use appropriate space allowances during mixing, provide enrichment to redirect aggressive behaviour, and mix pigs at life stages where hierarchy formation is less severe all reduce welfare harm. Systems that maintain stable social groups from birth to slaughter — difficult commercially but achievable in some production models — eliminate the repeated mixing welfare cost entirely.