Fecal cortisol metabolites indicate increased stress levels in horses during breaking in

Sport horses are frequently exposed to situations that were identified as stressors, indicated by an increased cortisol release, that might impair animal welfare. However, while many studies deal with the impact of exercise, transport and competition on stress in horses, there is only rare knowledge about the early phase of a horse’s sports career and studies investigating the stress level of young horses during breaking in are limited. To compare stress levels in unridden horses, horses during breaking in, and horses in training, we collected fecal samples of young, unridden horses (n=28) and of horses in different training stages (n=13) and measured fecal cortisol metabolite (FCM) concentrations. Our results showed that FCM concentrations of unridden horses were significantly lower than those of horses in training (Mann-Whitney Rank Sum Test, p<0.001). Particularly in the first year under the saddle FCMs were significantly higher than in unridden horses (One Way ANOVA + posthoc Holm-Sidak-Test, p<0.05), with a tendency of decreasing FCM levels with time in training. Furthermore, we observed that within the group of ridden horses, there was a larger range of variability in FCM levels, suggesting individual variations regarding their ability to deal with (training-induced) stress. These results indicate that breaking in is a stressful time for young horses, underlining the importance of carrying out the initial training as carefully as possible.