Behaviours exhibited during training predict physical tiredness in harness racing horses

Abstract Physical activity, especially high-intensity exercise, leads to physiological and behavioural changes. The objectives of this study were to investigate i) the effects of physical exercise on weight, behaviours, and head and ear positions on the days after low-intensity training (LIT) or high-intensity training (HIT) and ii) if behaviours, facial expressions, and/or physiological parameters (sweat, salivation and blood lactate levels) during training predict post-training behaviours. A total of 19 French trotter horses housed in four different training centers were studied the day before (Dpre) and after LIT or HIT (afternoon after training (Dtraining) and 2 days after training (D1Post and D2Post)). The results showed that horses exhibited i) longer durations of resting and head below the withers (HBW) on Dtraining and D1Post than on Dpre and ii) shorter eating durations on D1Post and D2Post than on Dpre after HIT. This was associated with significant weight loss on D2Post. Several behaviours and facial expressions associated with discomfort (e.g., head conflict behaviours, nose behind the vertical, and opened mouth), as well as amount of sweat, predicted the durations of resting, HBW and eating on D1Post. Thus, behaviours are impacted by training, and a combination of behaviours, facial expressions and visible physiological parameters exhibited during training could predict physical tiredness in harness racing horses.