Pigs and Group Housing Aggression Management

Social aggression at mixing events in group-housed pigs is a significant acute welfare problem that management strategies can reduce, though not eliminate, in commercial systems.

Key Facts

When unfamiliar pigs are mixed, aggression peaks in the first 24 to 48 hours as dominance hierarchies establish
Severe injuries including ear and tail wounds occur during mixing fights
Mixing at night, providing ample space, and using pheromonally familiar bedding reduces aggression intensity
Small, stable groups with no new introductions after establishment show dramatically lower chronic aggression
Anti-anxiety medication has been trialed at mixing to reduce acute aggression with some success
Some producers avoid mixing entirely through continuous production systems — welfare gains and losses are context-dependent

Welfare Considerations

Pig mixing aggression is an acute welfare event with predictable timing and manageable severity. The social complexity of pigs means that mixing unfamiliar individuals triggers intense dominance behavior that causes real injury. Management strategies that reduce mixing frequency, optimize mixing conditions, and provide retreat opportunities reduce — but do not eliminate — welfare costs. The most welfare-positive approach is systems design that minimizes the need for pig mixing in the first place: stable groups from weaning to slaughter that never require reintroduction. Where mixing is unavoidable, nighttime mixing, ample space, and substrate provision reduce the severity of aggressive interactions.

What You Can Do

Support farming certification standards that limit mixing events and require management protocols for aggression reduction
Choose pork from farms with stable group housing systems that minimize mixing
Advocate for research into management strategies that reduce mixing aggression in commercial pig production
Support development of pig housing designs that reduce mixing necessity
Engage veterinary advisors about mixing aggression management in existing pig operations