• horse;
  • exercise test;
  • lactate;
  • acclimation


Acclimation to treadmill exercise and to a respiratory gas collection mask were studied in 3 groups of Thoroughbred or Standardbred horses. Heart rate and plasma lactate concentration were measured at rest and at the completion of each speed increment during a series of acclimating runs at 4, 6 and 8 m/s on a treadmill inclined at a 10% slope. No significant differences were found in the heart rate at 4, 6 or 8 m/s between acclimating runs for any of the groups, except for a reduction between runs 1 and 2 at 4 m/s in a group of 19 racehorses that received 2 acclimating runs (Group 1). Heart rate values at 4 and 6 m/s were significantly higher during the subsequent exercise test in a group of 12 racehorses that received 4 prior acclimating runs (Group 3). Plasma lactate concentration was significantly reduced at 4 and 6 m/s from run 1 to 2 in Group 1 and at all speeds in a group of 6 experimental horses (Group 2) between run 1 and subsequent runs. There was also a significant reduction in plasma lactate concentrations at 6 and 8 m/s between runs 2 and 4 in Group 2 and between runs 3 and 4 at 8 m/s. A temperament scoring system was used to describe the behaviour of the horse on the treadmill. With the exception of 1 horse, the temperament score improved significantly, indicating acclimation to the treadmill after the first acclimating run in Groups 2 and 3. We conclude that acclimation occurred in the majority of horses after 1 or 2 exposures to treadmill exercise and a gas collection mask. However, there was substantial variability between horses and care must be taken when interpreting submaximal heart rate and plasma lactate data. This has important implications for the use of common measurements of exercise capacity such as V200 and VLA4, which rely on values obtained during submaximal exercise.