Larssen, R., Roth, L. S. V. 2022. Regular positive reinforcement training increases contact-seeking behaviour in horses. Applied Animal Behaviour Science 252, 105651.

Horses are commonly trained using negative reinforcement. However, a growing body of scientific evidence supports positive reinforcement as an efficient training method for horses. In this study we investigated the effects of adding a small but regular amount of positive reinforcement training to horses trained with negative reinforcement. A total of 36 privately owned horses not previously trained with positive reinforcement were divided into a training (N = 17) and a control (N = 19) group. The owners in the training group were asked to follow a training plan based on positive reinforcement for eight to nine weeks, in addition to their normal negative reinforcement training. The control horses continued with their usual negative reinforcement training. All horses were subjected to behavioural tests before and after the training period: a motionless human test to assess contact-seeking behaviour and a cognitive bias test to assess emotional state. Mane hair samples were obtained from all horses at the start and at the end of the training period to analyse hair cortisol concentrations as an expression of long-term stress. In addition, all owners filled out a questionnaire about their perceived relationship with their horses before and after the training period. We found that horses in the training group engaged in more physical contact (P = 0.050) with an unfamiliar person after the training period compared to before. The training group also tended to improve their owner-assessed relationship score (P = 0.072). They did not, however, show changes in their emotional state as assessed by the cognitive bias test (P > 0.1). Furthermore, we found no difference between the training and control groups in terms of hair cortisol concentrations. We conclude that a small but regular addition of positive reinforcement training can increase horses’ contact-seeking behaviour towards humans but is not enough to improve their emotional state or long-term stress levels.