Relationship between weight-carrying capacity and performance in a standardized treadmill exercise test in horses

Weight-carrying capacity is important in riding horses both for performance and welfare, yet there is no standardized method to estimate individual horses' weight-carrying capacity. This study investigated the correlation between the physiological response during a (i) standardized incremental exercise test (SET) on a treadmill and a (ii) ridden incremental weight-carrying exercise test (WET). Sixteen horses (15 ± 3 years) performed both tests, including four steps with increased speed or weight load, respectively. Body weight ratio (BWR) in the WET was 20%, 25%, 30%, and 35% in each step, respectively. Blood samples were collected after each step, and heart rate (HR) was recorded. The velocity (SET) and BWR (WET) at a HR of 180 and 190 bpm and plasma lactate concentration of 2, 3, and 4 mmol/L were estimated. There was a correlation (r = 0.92, p < 0.05) between the velocity at a plasma lactate concentration of 3 mmol/L (V_La3) in the SET and the BWR at a HR of 180 bpm (BWR₁₈₀) in the WET, but no other correlations were found. In conclusion, the SET was not applicable to estimate weight-carrying capacity in the horse. Further studies should investigate the importance of the correlation between V_La3 and BWR₁₈₀.