Development of a standard test to assess negative reinforcement learning in horses

•Negative reinforcement learning was evaluated in a pressure-release task using an algometer.•Force required for a correct response decreased with repetition on the first day.•More force was generally required on the right compared to the left side of the horse.•Horses appear unable to transfer learned responses to a tactile cue from one side to the other.

Most horses are trained by negative reinforcement. Currently, however, no standardised test for evaluating horses’ negative reinforcement learning ability is available. The aim of this study was to develop an objective test to investigate negative reinforcement learning in horses. Twenty-four Icelandic horses (3 years old) were included in this study. The horses were tested in a pressure-release task on three separate days with 10, 7 and 5 trials on each side, respectively. Each trial consisted of pressure being applied on the hindquarter with an algometer. The force of the pressure was increased until the horse moved laterally away from the point of pressure. There was a significant decrease in required force over trials on the first test day (P < 0.001), but not the second and third day. The intercepts on days 2 and 3 differed significantly from day 1 (P < 0.001), but not each other. Significantly stronger force was required on the right side compared to the left (P < 0.001), but there was no difference between first and second side tested (P = 0.56). Individual performance was evaluated by median-force and the change in force over trials on the first test day. These two measures may explain different characteristics of negative reinforcement learning. In conclusion, this study presents a novel, standardised test for evaluating negative reinforcement learning ability in horses.