Pig Mixing Aggression Welfare: Reducing Fighting When Pigs Are Grouped

Mixing unfamiliar pigs causes intense fighting as they establish social hierarchies, causing injuries and significant welfare harm. Management strategies to reduce mixing aggression are essential for pig welfare.

Key Facts

Mixing unfamiliar pigs causes biting, fighting, and skin lesion formation as hierarchies are established
The mixing period typically involves intense aggression for 24-72 hours before social stability emerges
Ear and tail biting wounds from mixing aggression create infection risks and chronic pain if untreated
Providing adequate space and multiple escape routes during mixing reduces severity of fighting
Mixing pigs in a novel environment rather than one pig's established territory reduces advantage and severity of fighting
Olfactory masking agents applied to all pigs at mixing reduce recognition-based attacks
Timing mixing to coincide with feeding diverts attention and reduces initial aggression intensity

Welfare Considerations

Pig mixing aggression is one of those welfare problems built into the production system: group housing requires social hierarchy establishment, and hierarchy establishment requires fighting. The welfare question is not how to eliminate this entirely but how to minimize its severity and duration. Evidence-based mixing management - novel environments, adequate space, escape routes, olfactory masking, and timing - can reduce the number and severity of injuries from mixing events. The welfare monitoring responsibility continues beyond mixing: wounds from fighting require treatment, and chronic low-level aggression in unstable groups requires investigation of resource provision adequacy. The most welfare-positive approach is consistent grouping from early life that minimizes the need for disruptive mixing events.

What You Can Do

Minimize mixing of unfamiliar pig groups and maintain stable social groups throughout production where possible
When mixing is necessary, use a novel environment rather than one established pig group entering another group territory
Provide adequate floor space and multiple feeding and drinking points during mixing to reduce resource competition
Apply olfactory masking sprays to all pigs before mixing to reduce recognition-based aggression
Monitor mixed pigs closely for 72 hours and treat any wounds from fighting promptly to prevent infection