Pig Aggression at Mixing: Prevention and Welfare Management

Mixing unfamiliar pigs triggers intense aggression that causes injuries, stress and welfare compromise lasting days to weeks, and is one of the most significant and preventable welfare challenges in modern pig production.

Key Facts

Pigs establish dominance hierarchies through fighting when mixed with unfamiliar animals
Mixing-induced aggression causes skin wounds, ear tears and tail injuries that can become infected
The most severe aggression occurs in the first 24-48 hours after mixing but elevated stress persists for up to a week
Aggression at mixing is responsible for significant economic losses through injury, reduced growth and increased mortality
Stable group housing throughout production — without mixing — substantially reduces aggression-related welfare problems
Mixing in dark, complex environments with multiple escape routes and hiding places reduces injury rates
Boar scent and novelty odour application before mixing can reduce aggression in some systems
Space allowance significantly affects post-mixing aggression severity — more space means less fighting

Welfare Considerations

Mixing-induced aggression causes acute pain from bite wounds, exhaustion from sustained fighting and chronic stress from subordinate status in a new hierarchy. Animals that lose fights face persistent harassment and reduced access to feed and water. The normalisation of post-mixing injury in many production systems means that significant suffering is treated as an unavoidable management cost rather than a welfare failure requiring active intervention. Evidence-based interventions including stable group housing, adequate space, environmental complexity at mixing and temporary aggression-reducing interventions are underutilised. The welfare benefits of reducing mixing-induced aggression are large given the number of pigs affected globally.

What You Can Do

Support pig welfare certification standards that require stable group housing and mixing management protocols
Advocate for space allowances that reduce post-mixing aggression severity
Encourage farmers to adopt environmental complexity measures at mixing such as barriers and multiple feed points
Reduce pork consumption or choose higher-welfare products from farms with documented mixing management
Support research into practical aggression reduction interventions scalable to commercial production
Raise awareness that pig aggression at mixing is a major and underappreciated welfare issue