Managing Pig Aggression During Group Mixing

Evidence-based strategies to reduce aggression and welfare harms when mixing pig groups at weaning, nursery, and finisher stages.

Key Facts

Mixing unfamiliar pigs triggers intense fighting lasting 1-3 days as new hierarchies form
Injuries from mixing can include skin lacerations, eye injuries, and vulvar biting in sows
Darkness during mixing reduces visual aggression cues and can reduce fighting severity
Salt-lick blocks and novel enrichment distract pigs from aggression during mixing
Larger pen space during mixing reduces fighting by allowing subordinate pigs to escape

Welfare Considerations

Pig mixing aggression is a major and recurring welfare event in commercial production. Each time groups are reorganized - at weaning, nursery entry, and finishing - animals must re-establish social hierarchies through fighting. This creates predictable periods of intense welfare harm that can be reduced but not eliminated with current management systems. Evidence-based mitigation includes timing mixing to reduce stress (evening rather than morning), providing additional enrichment materials, and ensuring adequate space so that subordinate pigs can avoid persistent attackers.

What You Can Do

Support farms minimizing unnecessary group mixing throughout the production cycle
Advocate for mixing management standards in pig welfare certification
Choose pork from systems demonstrating stable group management
Support research into effective aggression reduction strategies at mixing
Share evidence-based mixing management practices with pig farming communities