What is reinforced? The timing of the release of rein tension and the horse’s response latency for trot to walk transitions

Rein tension signals are commonly used to communicate with a horse during riding. In accordance with the principles of negative reinforcement, tension on the reins acts as signals and motivates a horse to change behavior, while release of rein tension reinforces the correct behavior. The aim of this study was to investigate if the features of rider rein tension signals and timing of the release have effects on the magnitude of rein tension, horse response latency, as well as horse behavior and head posture, during downward transitions. Nine riders rode the same eight horses in a crossover design, making eight transitions from trot to walk with each horse. Rein tension was measured and from video recordings the timing of the riders’ application of the decelerating rein signal and of the release were registered along with gait, behavior and head posture. Analyzing data using linear mixed models, it was found that median and minimum rein tension (p = 0.001) increased during the rein tension signal, compared to in trot before the transition. During the release median (p < =0.001) and maximum rein tension (p < 0.0001) decreased compared to during the rein tension signal. Interestingly, the timing of the release in relation to the downward transition varied among riders. The release was, in most cases, given ‘during’ the downward transition (70 %). However, in 19 % of the trials, the release was given ‘before’ the transition had begun, during the trot, and in 11 % the release was given ‘after’ the transition had ended, during the walk. Releasing rein tension ‘before’ the transition had begun was associated with longer response latency (p < 0.05). Maximum rein tension was lower at the fifth and eighth trial compared to the first (p = 0.02). Horse head movements were generally associated with lower magnitudes of rein tension when present compared to absent, while open mouth was associated with higher maximum rein tension. Since rein tension acts on the sensitive structures of the horse’s mouth and/or head/nose, further research on ways of reducing rein tension magnitude would benefit equine welfare. There is also room for further research on the implementation of cues, in isolation and together, to investigate riders’ communication via the reins as well as how to effectively implement learning theory into practice for riders on all levels.