Pig Aggression During Group Mixing

Mixing unfamiliar pigs together triggers intense aggression as animals establish dominance hierarchies, causing injuries, stress, and welfare harms that can be reduced through improved housing and management.

Key Facts

Pigs establish stable social hierarchies but introduction of unfamiliar animals triggers serious fighting
Mixing at weaning, regrouping, and transport are the highest-risk periods for aggression
Mixing injuries include ear and flank biting, skin lacerations, and occasionally fatal attacks
Providing additional space, substrate, and feeding points reduces fighting intensity at mixing
Boar odour sprays and tranquillisers are used commercially to reduce mixing aggression
Straw bedding reduces aggression by providing rooting substrate that redirects behaviour

Welfare Considerations

Aggressive encounters when pigs are mixed cause acute pain, fear, and stress. Wounds from biting can become infected, leading to chronic pain. Subordinate pigs may be unable to access food and water freely, leading to poor body condition. The welfare impact of mixing is compounded in barren environments with limited space and no substrate for redirected behaviour. Stable social groups, established early and maintained throughout the production cycle, dramatically reduce this welfare problem. Producers who minimise regrouping, provide adequate space, and use environmental enrichment at mixing significantly improve welfare outcomes without sacrificing productivity.

What You Can Do

Support producers using stable social groups and minimising regrouping throughout pig production
Choose higher welfare pork from systems providing adequate space and environmental enrichment
Advocate for housing standards requiring sufficient space and enrichment to reduce mixing aggression
Back research into pheromone-based and management strategies reducing mixing stress in pigs
Support farm welfare programs training producers in low-stress pig handling and mixing techniques