Pigs are highly social animals and the disruption of established social groups through mixing causes intense aggression and stress that remains one of the most significant welfare challenges in commercial production.
Social group mixing is one of the most prevalent and impactful welfare stressors in commercial pig production. The need to sort animals by weight, manage feed access, and move pigs between production facilities creates repeated disruption of established social bonds and forces repeated aggressive resolution of dominance. Each mixing event causes a wave of fighting, injury, and stress that is entirely predictable and to a considerable degree avoidable. Strategies for reducing mixing stress include stable group formation from early ages, olfactory familiarity techniques before mixing, careful physical environment design to allow avoidance behaviour, and minimising the number of mixing events across the production cycle. Producer education and system design are the primary levers for welfare improvement in this area.