Managing Pig Aggression: Evidence-Based Strategies

Pig aggression during mixing events causes injuries, stress, and welfare harm, and evidence-based strategies significantly reduce its incidence and severity.

Key Facts

Pigs establish dominance hierarchies through aggression when unfamiliar animals meet
Mixing aggression is most intense in the first 24-48 hours after group formation
Injuries from fighting include ear and flank wounds, eye trauma, and in severe cases death
Environmental factors including space, resources, and novelty influence aggression severity
Darkened pens during mixing reduce the visual stimuli that trigger aggression
Providing novel objects during mixing redirects investigative behavior from pen mates
Olfactory masking (cider vinegar spray) reduces olfactory identification and slows hierarchy establishment

Welfare Considerations

Mixing aggression causes acute, severe suffering - biting, fighting, and sustained attacks on weaker individuals. The most effective welfare intervention is preventing unnecessary mixing. When mixing is unavoidable, evidence-based mitigation strategies reduce aggression duration and injury severity. Providing extra space, novel enrichment, ad libitum feed, and dim lighting during mixing events reduces both attack rates and injury severity. Post-mixing surveillance to identify and remove severely injured individuals prevents ongoing suffering.

What You Can Do

Minimize unnecessary pig group mixing throughout the production cycle
Implement darkened housing during the first 24 hours after mixing events
Provide novel enrichment materials at mixing to redirect investigative behavior
Ensure ad libitum access to feed and water during mixing to reduce resource competition
Monitor intensively during the first 48 hours after mixing and remove injured animals promptly