Pig Social Hierarchy and Mixing Welfare

Pigs have complex social structures and the process of mixing unfamiliar pigs — unavoidable in commercial production — causes intense aggression and welfare suffering that appropriate management can reduce.

Key Facts

Pigs establish linear dominance hierarchies through fighting; mixing unfamiliar groups triggers renewed fighting
Aggression at mixing causes injuries including facial lacerations, ear biting, and limb wounds in both aggressors and victims
Mixing events that occur at weaning, rehousing, and regrouping at different production stages accumulate welfare harm
Olfactory familiarisation — exposing pigs to the smell of unfamiliar pigs before direct contact — reduces initial aggression
Mixing in familiar or novel environments (rather than dominant pigs' home territory) reduces severity of aggression
Higher space allowances at mixing significantly reduce aggression intensity and duration by allowing more escape opportunities

Welfare Considerations

Pig mixing aggression is one of the most predictable and frequent sources of acute welfare harm in commercial pig production. Injuries sustained during mixing fights cause pain, skin wounds with infection risk, and in severe cases, death of subordinate individuals unable to escape. The cumulative welfare burden across a production cycle — multiple mixing events from birth to slaughter — is substantial. Management strategies that reduce aggression severity (olfactory familiarisation, adequate space, novel mixing environments) are available but not universally implemented. Stable litter groups maintained from birth through slaughter — which would eliminate mixing events entirely — are feasible in some production systems and produce dramatically better welfare outcomes.

What You Can Do

Support pork assurance schemes that require stable group management from birth to slaughter to eliminate regrouping mixing events
Choose pork from outdoor or free-range systems with higher space allowances that reduce aggression severity at inevitable mixing points
Advocate for maximum regrouping frequency standards in pig welfare legislation to limit the number of stressful mixing events
Support research into effective low-cost olfactory familiarisation protocols that small and medium pig farms can implement