Farmed Pig Social Mixing Aggression Management

Mixing unfamiliar pigs causes intense, sustained aggression that is one of the most acute welfare harms in commercial pig production, requiring evidence-based management strategies.

Key Facts

Pigs establish stable dominance hierarchies within groups but respond aggressively to unfamiliar individuals - mixing unfamiliar groups triggers extended fighting lasting hours to days.
Injuries from fighting at mixing include bite wounds to ears, flanks, and tails that become infected and cause chronic pain.
The commercial practice of mixing pigs from multiple litters or groups at weaning, growing, and finishing stages creates repeated aggression events across an animal's life.
Olfactory signals are primary in pig social recognition - temporary disruption of smell signals using novel odors applied to all pigs at mixing reduces but does not eliminate aggression.
Providing adequate space, escape routes, and physical barriers at mixing reduces injury severity, as subordinate animals can withdraw from dominant individuals.

Welfare Considerations

Social mixing aggression in pigs is inherent to commercial production systems that require regrouping at multiple life stages, but its welfare impact can be substantially mitigated by management practices. The key principles are providing adequate space at mixing, including physical barriers and escape routes, mixing during low-light periods to reduce arousal, and monitoring pigs closely in the 48-72 hours following mixing to remove severely injured individuals. Stable social groups maintained throughout production significantly reduce cumulative welfare harm. Systems that minimize the number of mixing events across a pig's life offer better welfare outcomes than those requiring frequent regrouping.

What You Can Do

Support producers using stable social groups that minimize mixing events across the production cycle.
Advocate for space allowances that allow subordinate pigs to escape aggression at mixing.
Engage with welfare assurance schemes that include mixing management protocols.
Support research into olfactory and other non-painful methods of reducing mixing aggression.