Fecal Cortisol Metabolites Indicate Increased Stress Levels in Horses During Breaking-In: A Pilot Study

Abstract

Sport horses are frequently exposed to situations that were identified as stressors, indicated by an increased cortisol release, which might impair animal welfare. However, while many studies deal with the impact of exercise, transport, and competition on stress in horses, little is known 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 preliminary 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 + post hoc Holm-Sidak test, p < 0.05), with a tendency for FCM levels to decrease 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.

Keywords: equestrian sports; equine; feces; glucocorticoids; riding; stress; training.

Figure 1

FCM concentrations of unridden horses (yellow box, n = 13) were significantly lower than of horses in training (green box, n = 28). Boxplots represent median FCM concentrations (line) in the different age groups ± 25th and 75th percentiles (box) and with the 10th and 90th percentiles shown (whiskers). Outliers are marked by dots. *** p < 0.001, Mann–Whitney rank sum test.

Figure 2

Newly broken-in horses had higher FCM concentrations compared to unridden horses. Horses that have been ridden for less than one year had significantly higher FCM levels than horses that were not yet broken-in. After more than one year in training there was no statistical difference between FCM levels in horses in training (green boxes) and unridden horses (yellow boxes). Boxplots represent median FCM concentrations (line) in the different age groups ± 25th and 75th percentiles (box) and 10th and 90th percentiles (whiskers). Outliers are indicated by dots. Different letters indicate significant differences between groups, p < 0.01, one way ANOVA + post hoc Holm–Sidak test.

Figure 3

Relation between FCM levels of individual horses and the time (months) before and after breaking-in, respectively.