Farmed Pig Group Housing Aggression Management

Managing aggression in group-housed pigs is a significant welfare challenge, particularly at mixing events when unfamiliar pigs must establish new social hierarchies.

Key Facts

Mixing of unfamiliar pigs triggers intense fighting as social hierarchies are established
Mixing-induced aggression peaks in the first 24-72 hours and can cause serious injury
Submissive pigs may be prevented from accessing food and water during hierarchy establishment
Stable social groups show minimal aggression once hierarchies are established
Smell-based methods including using a common odor or pheromone sprays reduce fighting
Mixing under low light or at feeding reduces aggression in some studies
Space allowance affects the severity of mixing aggression - more space reduces injury
Providing escape routes and barriers allows submissive pigs to avoid aggressive individuals

Welfare Considerations

Mixing aggression causes acute welfare harm through physical injury from biting and impact injuries, and through the stress of intense social conflict. Submissive pigs that cannot escape aggressive individuals face sustained physical punishment and resource exclusion. Skin lesions from bite wounds and impact injuries are standard welfare indicators used in pig welfare assessments, reflecting the frequency of this welfare problem in commercial systems. Once social hierarchies are established, welfare improves substantially in stable groups with adequate resources. Management strategies that minimize mixing events - maintaining stable social groups from weaning through slaughter - represent the most effective approach to reducing mixing aggression welfare costs. When mixing is unavoidable, providing additional space, escape routes, and using chemical or lighting strategies reduces injury severity.

What You Can Do

Support production systems that minimize social regrouping of pigs
Choose pork from welfare-certified farms with demonstrated mixing aggression management
Advocate for regulations requiring escape routes and adequate space during pig mixing
Learn about pig social behavior and the welfare implications of mixing
Reduce pork consumption to decrease demand from intensive systems with frequent mixing
Support research into effective strategies for reducing mixing aggression in commercial pig systems