Voluntary Rein Tension in Horses When Moving Unridden in a Dressage Frame Compared with Ridden Tests of the Same Horses—A Pilot Study

SIMPLE SUMMARY: The aim of this pilot study was to evaluate the maximum rein tension that horses voluntarily adopt when wearing side reins set in dressage frame without a rider, and to compare that to rein tension in dressage frame with a rider. Without a rider, all horses maintained a rein tension force of approximately 1 kg in all gaits. For the same horses with a rider, rein tension force was significantly higher at approximately 3 kg on each side to maintain the dressage frame. Understanding and lowering the peak forces acting on the mouth of the horse could enhance equine welfare in daily riding practice. ABSTRACT: Too much rein tension while riding may compromise the welfare of the horse. But who generates the tension on the reins—the horse or the rider? The primary aim of this pilot study was to evaluate the maximum rein tension that horses voluntarily maintain without a rider compared to rein tension with a rider. A secondary aim was to evaluate conflict behaviours in relation to rein tension. Thirteen horses were used, all fitted with customised “Animon” rein tension sensors (25 Hz, up to 600 N range), free-moving with side reins set in dressage competition frame with the noseline on the vertical. Rein tension was measured at the walk, trot, and canter in both directions in a round pen. The same horses were then ridden by their usual riders and completed the same task on a riding ground. Continuous video recordings were obtained to subsequently quantify the occurrence of conflict behaviours. The difference in mean maximum peak of rein tension with and without a rider for each gait was compared using the Wilcoxon Rank Sum test. Without a rider, rein tension was significantly lower (Wilcoxon T = 0, p < 0.01, 7.5 N ± 2.8 N) than with a rider (Wilcoxon T = 0, p < 0.01, 24.0 N ± 12.3 N). Regardless of the different rein tensions in the ridden exercise, all of the horses exhibited approximately the same amount of rein tension in the unridden exercise. The frequency of conflict behaviour was higher with a rider than without (11 ± 14 per minute vs. 2 ± 3 per minute; T = 4, p < 0.01).