Managing pigs in dynamic groups — where animals are regularly mixed — is one of the most challenging aspects of group housing welfare, as mixing triggers aggression and stress.
The welfare cost of frequent mixing in commercial pig systems is substantial and well-documented. Each mixing event inflicts injury and stress on the most vulnerable animals — those unable to compete for dominance position. Static group systems that maintain stable social groups from weaning avoid this repeated trauma and represent the highest welfare standard for group housing. When mixing is unavoidable — such as at regrouping or transfer points — providing adequate space, visual barriers, and monitoring for severe aggression limits the worst welfare outcomes. Welfare standards and audits should track mixing frequency and injury rates as key indicators.