Rein tension acceptance in young horses in a voluntary test situation.

REASONS FOR PERFORMING THE STUDY During riding, horses are frequently exposed to pressure from the rider, e.g. through the bit and reins, but few studies have investigated at which point rein tension becomes uncomfortable for the horse. OBJECTIVES To investigate how much rein tension young inexperienced horses are willing to accept in order to obtain a food reward; whether the tension acceptance changes during 3 consecutive test days; and whether rein tension correlates with the expression of conflict behaviour and heart rate. HYPOTHESES Pressure-naïve horses will apply only little rein tension in the first voluntary trial, but their acceptance will gradually increase. High levels of rein tension will lead to expression of conflict behaviour and increases in heart rate. METHODS Fifteen 2-year-old, bridle-naïve mares were encouraged to stretch their head forward (across a 0.95 m high metal bar) to obtain a food reward in a voluntary test situation. On each test day, each horse was exposed to 2 control sessions (loose reins), an intermediate and a short rein session (1 min/session). Rein tension, heart rate and behaviour were recorded. RESULTS The horses applied significantly more tension on the first day (mean rein tension: 10.2 N), compared to the second and third test day (Day 2: 6.0 and Day 3: 5.7 N). The horses showed significantly more conflict behaviour in the short rein treatment. There was no treatment effect on heart rate. CONCLUSIONS AND POTENTIAL RELEVANCE The horses applied the highest rein tension on the first day, and apparently learned to avoid the tension, rather than habituate to it. Rein tension correlated with expression of conflict behaviour, indicating that the horses found the tension aversive. Further studies should focus on the correlation between rein tension and conflict behaviour in ridden horses.