A note on the effect of a palatable food reward on operant conditioning in horses

We investigated the effect of two food types (hay or pellet) on operant conditioning of 12 horses. One group was trained using pelleted concentrate (Group P) and the second (Group H) was trained using cut timothy hay as rewards. We investigated the effect of the food type on the time needed to complete the operant conditioning. There was no difference between the groups in the time needed to complete the operant conditioning (P = 0.78). Following completion of the operant conditioning, 10-min trials were conducted on five consecutive days. On the 2nd and 3rd days the food rewards (P and H) were switched for the two groups, and on the 4th and 5th days the food rewards were returned to the original type. When the food reward was changed from P to H, the mean number of rewards obtained decreased significantly in Group P (the 1st day (121.8) versus the 2nd day (45.4) and the 3rd day (39.4), P < 0.05, respectively) and tended to decrease in Group H (the 3rd day (120.4) versus 4th day (80.8), P = 0.06). The change induced the extinction of operant responses in three horses in Group P. When the food reward was changed from H to P, the mean number of rewards obtained increased significantly in Group P (the 3rd day (39.4) versus the 5th day (105.4), P = 0.10) and Group H (the 1st day (62.2) versus the 3rd day (120.4), P < 0.01). These results suggest that the palatability of the food reward may not improve the time required to train horses, but changing the food reward from a more palatable to a less palatable food may decrease the number of operant responses in horses, and extinguish them in some horses that were initially conditioned using a more palatable food. These results also suggest that whatever food reward is initially used in operant conditioning protocols in the horse may be important if it is necessary to subsequently change the food reward.