Play behaviour in pigs is an important positive welfare indicator whose occurrence signals that animals are experiencing states beyond mere absence of suffering.
The Five Domains model of animal welfare, now superseding the Five Freedoms, emphasises the importance of positive welfare states as well as absence of negative ones. Play behaviour in pigs is one of the best-validated indicators of positive welfare, occurring only when animals feel safe, healthy, and unstressed. The near-absence of play behaviour in standard intensive pig systems is a welfare indicator in itself, suggesting chronic stress or deprivation that prevents normal positive affect expression. Enrichment that elicits play is both a welfare intervention and a monitoring tool.