Mixing unfamiliar pigs triggers intense aggression as animals establish dominance hierarchies, and managing this transition welfare challenge is critical for group housing success.
Mixing aggression represents a significant welfare challenge in group pig housing that is often underestimated in its severity. Pigs that cannot escape attackers sustain lacerations, bite wounds, and occasionally serious injuries. Subordinate animals may be prevented from accessing feed and water during the post-mixing period. Careful management of mixing events — timing, environment, and group composition — substantially reduces aggression severity. The evidence strongly favours maintaining stable social groups from weaning rather than repeatedly regrouping animals for management convenience. Stable groups also show better performance and reduced stress hormone concentrations throughout the production cycle.