Heart rate responses during acclimation of horses to water treadmill exercise

Reasons for performing study: The use of water treadmill exercise in horses is popular, although little is known about the physiological responses to this form of exercise. No information exists regarding the time taken to acclimate to water treadmill exercise compared to that of high-speed treadmill exercise, for both physiological and biomechanical parameters. Objective: To determine heart rate responses during acclimation to water treadmill exercise with and without sedation on first time exposure. Methods: All horses were exercised on a water treadmill at the walk for 15 min once a day for 4 days. Fourteen horses (mean ± s.d. age 9 ± 3.2 years) were assigned randomly to Group A (sedated) and Group B (nonsedated). Group A were given 20–30 μg/kg bwt romifidine within 10–15 min prior to the start of the first acclimating run. Acclimation was determined by the time taken to reach a threshold heart rate value. Results: Group A and B reached threshold heart rate values by the 6th minute of the 4th run (72.8 beats/min) and the 6th min of the 3rd run (78.7 beats/min), respectively. No significant difference was found (P>0.05) between Group A and B in the time taken to reach threshold heart rate values. Acclimation to water treadmill exercise requires a minimum of 2 times 15 min nonsedated acclimating runs. Sedation can be used to prevent horses panicking during the first exposure but thereafter does not affect the time taken to acclimate. Potential relevance: Previous experience of water treadmill exercise should be taken into consideration prior to collecting physiological and biomechanical data. Further studies detailing the physiological and biomechanical responses are required prior to making recommendations for the incorporation of this mode of exercise into rehabilitation programmes.