Frequent riding sessions daily elevate stress, blood lactic acid, and heart rate of Thoroughbred riding horses

Minimizing stress in horses used in horse riding programs is necessary from an animal health and welfare perspective. The goal of this study was to determine the recommended horse riding frequency per day for horse riding clubs. Five Thoroughbred riding horses were rested (no riding) or ridden in 1, 2, or 4 forty-five–minute horse riding sessions per day by qualified riders for 5 weeks. For the assessment of stress, the ratio of neutrophil (N) to lymphocyte (L) was monitored 2 h after the last session. Blood lactic acid level and heart rate were determined immediately after horse riding. Blood was collected 1 day before and 17 h after horse riding for the baseline and recovery rate, respectively. The neutrophil:lymphocyte ratio, heart rate, and lactic acid levels sampled from horses ridden for four horse riding sessions were significantly higher than the levels of horses at rest. In contrast, these values for horses ridden one to two times a day showed no significant difference compared with the levels for a horse at rest. Interestingly, the frequency of bucking was significantly higher during the first horse riding session compared with that of the second or fourth horse riding sessions. It was concluded that (1) horses become more stressed when ridden four times a day than when ridden one to two times a day, and they may need a longer time to recover their health status. Furthermore, (2) horses showed a tendency of bucking during the first horse riding session after a 1-day confinement in the stable.