Mixing unfamiliar pigs causes significant aggression and welfare harm. Understanding the causes of pig social conflict and evidence-based management strategies is essential for producers.
Pig mixing is an almost unavoidable feature of commercial pig production, yet each regrouping event causes a period of acute welfare compromise as a new social hierarchy is established through fighting. The welfare impact of mixing is proportional to the intensity and duration of aggression, the injuries sustained, and the ongoing stress for subordinate animals who lose hierarchical contests. Management strategies that reduce mixing frequency — maintaining stable social groups from weaning to slaughter — represent the gold standard but are difficult to achieve in complex production systems. Where mixing cannot be avoided, environmental management can reduce its severity: sufficient space to avoid and escape, multiple feeding and drinking points to reduce competition, and mixing in novel pen environments where no individual has established home advantage.