Farmed Pig Aggression and Mixing Welfare

Pig aggression during group mixing causes injury, stress and subordination-related welfare problems that require careful management throughout the production cycle.

Key Facts

Pigs establish social hierarchies through fighting when unfamiliar groups are mixed
Initial mixing fights can last hours and cause significant injuries including skin lesions and ear damage
Regrouping stress causes cortisol elevation lasting 24-72 hours after mixing
Stable groups with minimal mixing have significantly lower aggression and better welfare outcomes
Providing adequate space during mixing allows subordinate animals to avoid dominant individuals
Olfactory familiarity techniques including bedding mixing before physical contact can reduce aggression
Anti-agonistic sprays have variable and generally modest effects on mixing aggression
Mixing at night reduces visual cues and may reduce initial fighting intensity

Welfare Considerations

Group mixing aggression is one of the most significant acute welfare challenges in pig farming. The pain of biting wounds, stress of social defeat for subordinate individuals, and chronic stress of integration into new groups represent substantial welfare costs. Production system design that minimises mixing - stable groups from weaning to slaughter - delivers the best welfare outcomes. Where mixing is unavoidable, management strategies that reduce aggression and provide space for flight responses meaningfully reduce welfare harm.

What You Can Do

Support pig welfare standards that require stable group management with minimal mixing
Choose pork products from free-range or outdoor systems with stable social group management
Advocate for stocking density standards that provide adequate space for mixing management
Support research into mixing management strategies with validated welfare outcomes
Engage with pork supply chains about their requirements for mixing management