Hold your horses: The effect of play behaviour in horses (Equus caballus) under imposed stress

Horses ( Equus caballus ) are prone to acute and chronic stress, particularly in equestrian sports, raising significant welfare concerns. We investigated whether and how play can mitigate acute acoustic stress and enhance decision-making in horses. We studied horses in two different stabling and working conditions (intensively vs. extensively managed) and recorded their behaviours in a Y maze for a food reward in three sequential treatments: baseline (no stressor), stress (exposure to a short-term acoustic stressor) and solitary object play with a large ball (exposure to the stressor followed by play). We recorded behavioural diversity, latency to approach the decision point (before choice) and food reward arm, behaviours associated with positive and negative emotional state and overall choices made (decisions) in the maze. Decision-making was significantly better in the play treatment than in both the baseline and stress treatments. Horses in the stress treatment exhibited a greater diversity of behaviours associated with negative emotional states and poorer decision-making compared to the play and baseline treatments. Additionally, intensively managed horses under more constrained conditions, were more stressed than those extensively managed. Our findings suggest that play can effectively reduce stress and improve decision-making in horses, depending on their housing conditions, and highlight the importance of play for equine welfare. • Stress linked to reduced behaviour diversity, negative emotional states, and poor decisions. • Play reduces stress and enhances decision-making in horses. • Horses from a riding school showed higher stress levels vs. farm-based horses. • Play improves welfare by mitigating stress and supporting better decision-making in horses.