Play is a positive welfare indicator in many species, and its presence or absence provides a reliable signal of animals experiencing good or poor welfare conditions.
The capacity for play reflects genuine positive experience — animals at play are not merely fulfilling biological functions but experiencing something like enjoyment. Welfare environments that allow play represent more than the absence of suffering; they represent genuine positive welfare states. The fact that play is reliably suppressed by negative welfare conditions means that providing conditions for play is not an optional extra but a marker of genuinely good welfare. Industries and laboratories that prevent play conditions are preventing positive wellbeing, not merely neutral states.