Aggression and Social Stress in Pigs

Aggression is a major welfare problem in intensive pig production, causing injury, fear, and chronic stress — particularly at mixing events when unfamiliar pigs are grouped together.

Key Facts

Mixing unfamiliar pigs triggers intense fighting for up to 24 hours as hierarchies are established
Injuries from mixing including ear tears, flank bites, and eye damage are common and painful
Tail biting is an expression of redirected aggression in barren environments
Aggression at the feeder is increased by competition when feeding space is inadequate
Castration, which reduces boar taint in meat, reduces aggression but causes acute pain without anaesthesia

Welfare Considerations

Pig aggression causes significant acute and chronic welfare harm. The immediate pain of fighting injuries is compounded by the chronic stress of living in unstable social groups where hierarchies must repeatedly be re-established. Management interventions — stable group composition, adequate feeding space, enrichment, and lower stocking density — all reduce aggression. Where mixing is unavoidable, providing dark areas for retreating, ample enrichment, and monitoring for serious injury reduces harm. Pen design and management quality have enormous influence on aggression-related welfare outcomes.

What You Can Do

Support certification standards that limit unnecessary pig mixing and require stable group management
Advocate for adequate feeding space requirements in pig housing regulations
Choose pork from certified higher-welfare producers with documented aggression management protocols
Support research into low-stress mixing strategies and pen design innovations
Educate others about the welfare impacts of pig social stress in intensive systems