Regrouping pigs triggers severe aggression as animals re-establish social hierarchies, causing significant welfare harms that can be mitigated through management.
Aggression at regrouping causes physical injury, psychological stress, and impaired welfare for multiple days. The necessity of regrouping in commercial systems makes minimising this unavoidable stress a welfare priority. Evidence-based mixing protocols including timing, environment modification, and olfactory masking can substantially reduce aggression-related suffering.