Research has confirmed that pigs experience emotional contagion — the ability to share emotional states with other pigs — making the social conditions of commercial housing a welfare issue with direct psychological dimensions.
The capacity for emotional contagion in pigs means that the welfare of each pig in a group affects the welfare of others. A distressed pig creates measurable stress in its pen-mates. Commercial practices that mix unfamiliar pigs — at weaning, after transport, and at lairage — create cascading emotional stress across entire groups. Maintaining stable social groups is one of the most effective welfare interventions available, with benefits that compound through the social network.