Effects of rein tension on the behavior and physiology of horses during a standardized learning task

Rein tension is used to apply pressure to control both ridden and unridden horses. The pressure is delivered by equipment such as the bit, which may restrict voluntary movement and cause changes in behaviour and physiology. Managing the effects of such pressure on arousal level and behavioural indicators will optimise horse training outcomes. This study examined the effect of training horses to turn away from bit pressure on cardiac variables and behaviour (including responsiveness) over the course of eight trials in a standardised learning task. The experimental procedure consisted of a resting phase, treatment/control phase, standardised learning trials requiring the horses (n=68) to step backwards in response to bit pressure and a recovery phase. As expected, heart rate increased (GLM, F 1,66 =5.01, p<0.05) and heart rate variability decreased (GLM, F 1,66 =7.3, p<0.01) when the handler applied rein tension during the treatment phase. The amount of rein tension required to elicit a response during treatment was higher on the left than the right rein (t-test: t 30 =2.775, p<0.01). Total rein tension required for the subsequent trials reduced (REML, F 6,462 =6.10, p<0.001) sequentially, as did time taken (REML, F 1,41.7 =41.67, p<0.001) and steps taken (REML, F 6,462 =10.65, p<0.001). The probability of head tossing also decreased (F 11,730 =2.16, p<0.05) with the progression of the trials and was higher (F 1,72 =5.86, p<0.05) for the control horses than the treated horses. These results suggest that preparing the horses for the lesson and slightly raising their arousal levels, improved learning outcomes. Lay person message: The results of this study suggest that preparing horses by moderately raising their arousal levels before lessons, could improve training. Horses in this study showed increases in arousal (indicated by moderate cardiac changes), followed by an immediate return to resting rates after the lesson. We propose that, in the future, this technique could be referred to as bringing horses into the engagement zone.