Heart rate and heart rate variability responses during three exercise tests and recovery in horses participating in the Fédération Équestre Internationale Eventing World Challenge.

Abstract

BACKGROUND: Horses competing in eventing competitions encounter significant challenges that increase their risk of severe injuries and metabolic disorders. Numerous studies have focused on the risk of such injuries and disorders during the cross-country segment. While one study has examined autonomic responses during this segment, research on these responses across all three phases of competition, particularly during one-day events, is still limited. The objective of this study was to analyse the autonomic responses of horses by measuring heart rate (HR) and heart rate variability (HRV) during three exercise tests and their recovery while competing in the F&#xe9;d&#xe9;ration &#xc9;questre Internationale Eventing World Challenge. HR and HRV were monitored in 10 horses during the competition; however, data were collected from only nine horses, as one was eliminated. RESULTS: Beat-to-beat (RR) interval decreased from control (1742&#x2009;&#xb1;&#x2009;202.3 ms) during dressage (D), jumping (J) and cross-country (CC) tests, lasting 60&#xa0;min after cross-country (60-CC) (D: 594.6&#x2009;&#xb1;&#x2009;40.2 ms, J: 420.6&#x2009;&#xb1;&#x2009;94.5 ms, CC: 358.0&#x2009;&#xb1;&#x2009;66.9 ms and 60-CC: 1424.2&#x2009;&#xb1;&#x2009;98.3 ms vs. control: 1742.0&#x2009;&#xb1;&#x2009;202.3 ms, p&#x2009;<&#x2009;0.05-0.001). HR increased during the exercise tests, extending to 60-CC (D: 101.4&#x2009;&#xb1;&#x2009;7.0 beats/min, J: 148.2&#x2009;&#xb1;&#x2009;30.5 beats/min, CC: 172.0&#x2009;&#xb1;&#x2009;27.0 beats/min and 60-CC: 42.2&#x2009;&#xb1;&#x2009;3.0 beats/min vs. control: 34.8&#x2009;&#xb1;&#x2009;3.7 beats/min, p&#x2009;<&#x2009;0.05-0.001). Various HRV metrics were lower during J than D, including standard deviation of normal-to-normal RR interval (D: 25.4&#x2009;&#xb1;&#x2009;9.1 ms vs. J: 9.8&#x2009;&#xb1;&#x2009;6.2 ms, p&#x2009;<&#x2009;0.01), total power band (D: 512.4&#x2009;&#xb1;&#x2009;261 msvs. J: 126.8&#x2009;&#xb1;&#x2009;180.4 ms, p&#x2009;<&#x2009;0.05) and standard deviation 2 (D: 35.0&#x2009;&#xb1;&#x2009;12.5 ms vs. J: 13.4&#x2009;&#xb1;&#x2009;8.9 ms, p&#x2009;<&#x2009;0.01). Changes in the parasympathetic and sympathetic nervous system indices corresponded with RR interval and HR modifications, respectively. CONCLUSIONS: The study found that autonomic responses were significantly pronounced during three exercise tests, with notably stronger reactions observed during the jumping and cross-country segments of the Eventing World Challenge. This preliminary study provides valuable insight into the autonomic regulation of horses during these phases of one-day eventing competitions.