Introducing pigs to new groups causes aggression and stress until new hierarchies are established. Understanding how to minimise welfare impacts during necessary mixing is important for farm management.
Social mixing represents one of the most acute welfare events in commercial pig production, causing brief but intense physical conflict and injury. The welfare harm is proportional to the stocking density in which mixing occurs, the presence of resources that must be competed for, and the lack of escape routes and refuges. Management techniques that reduce the intensity and duration of post-mixing aggression significantly reduce welfare harm. Pre-mixing exposure to common scents, adequate space with multiple resources, dim lighting, and appropriate mixing timing all contribute to reduced injury rates. The genetic temperament of pigs affects aggression propensity, and selecting calmer genetics reduces the welfare impact of necessary mixing events without eliminating the underlying territorial behaviour that drives them.