Horse mouth behaviour related to selected kinematic variables representing horse-rider interaction

The objective of this pilot study was to investigate the influence of rein contact and the movement of the rider’s hand on the horse’s behaviour, analysing data on horses ridden in two different head and neck positions. We hypothesized that the rider’s hand movements and rein tension generate behavioural responses from the horse, and more so when ridden on the bit compared to free and unrestrained. Data were collected from seven dressage horses/riders in sitting trot on a high-speed treadmill. Kinematics were recorded using a 12-camera, infrared-based opto-electronic system. Behavioural recordings were made from video and three horses wore a rein tension meter. After stride split, data were standardised to 0-100% stride duration. Mixed models were used to analyse how the behaviours varied over the stride cycle; trial within horse was treated as a random effect, while percentage of stride, rein tension and kinematic variables mainly related to the rider’s hand were entered as fixed effects. Behaviours discerned were lip movement, mouth movement, open mouth, ear position, head tilt and tail movement. Mouth movements were associated with the suspension phase of the trot and percentage of stride was highly significant (P<0.0001). Head and neck position was non-significant in the final models, while rein tension and the distance between the rider’s hand and the horse’s mouth affected the amount of mouth movements. The results from this preliminary study convey the large variations between horses and riders, as well as the complexity of the interaction.