Play behavior in pigs is a reliable indicator of positive welfare states, and its absence signals chronic stress or deprivation.
Play is a luxury behavior that animals engage in only when their immediate needs are met — it signals the presence of positive affect. The near-absence of play in barren commercial pig environments is therefore meaningful evidence of poor welfare. Interventions that restore play behavior in pigs — enrichment, more space, better social conditions — are directly improving their subjective experience.