Social Hierarchy and Mixing Stress in Pigs

Pigs establish clear social hierarchies through aggression when mixed with unfamiliar individuals, and the welfare implications of mixing practices in commercial pig production are significant and manageable.

Key Facts

Mixing unfamiliar pigs causes a predictable aggression peak lasting 12-48 hours as hierarchy is established
Mixing at weaning is the most welfare-compromising event due to multiple simultaneous stressors
Skin lesion scoring provides an objective measure of mixing-related aggression in commercial systems
Stable boar groups show significantly lower aggression than mixed groups
Providing additional space, hiding opportunities, and escape routes at mixing reduces welfare harm

Welfare Considerations

Mixing stress causes acute injury and prolonged anxiety in pigs. The establishment of social dominance through biting, pushing, and fighting results in wounds that can become infected and lesions that persist for days. In commercial systems, multiple mixing events through the production cycle expose pigs to repeated social disruption. Management strategies including stable group composition, large pen size, and provision of resources that allow subordinates to avoid dominant animals substantially reduce the welfare burden of inevitable mixing events.

What You Can Do

Advocate for management systems that minimise regrouping of pigs through the production cycle
Support farms implementing stable group management from weaning to slaughter
Choose pork from producers certified to schemes that specify mixing management requirements
Engage with pig welfare research on identifying and implementing effective mixing stress reduction strategies