Effects of short-term training on thermoregulatory and sweat responses during exercise in hot conditions

P>Reasons for performing study: There is evidence that extensive training in cool conditions results in improvements to heat dissipation that contribute to successful acclimatisation. In horses, the effects of a less extensive training regimen have not been determined. Objective: This study investigated whether 10 consecutive days of moderate intensity treadmill training in cool conditions would improve thermoregulatory and sweating responses of horses to exercise in the heat. Methods: Six unfit Thoroughbred horses completed a standardised treadmill exercise test (SET) in hot, dry conditions (32-34 degrees C, 45-55% RH) before (SET1) and after (SET2) 10 consecutive days of running at 55% VO2max for 60 min in cool conditions (19-21 degrees C, 45-55% RH). Each SET consisted of a 5 min warm-up and cool down at a walk, 40 min of trotting (50% VO2max), 7 min at 75% VO2max and a 30 min standing recovery. Bodyweight was determined pre- and post SET. Heart rate, rectal, skin, pulmonary artery and muscle temperatures were measured throughout the SETs and sweating rate (SR) and sweat ion losses determined for each 5 min interval. Results: Following training, mean VO2max increased by 8.9% (P < 0.05). In SET2, PCV was lower during the last 30 min of exercise and end-exercise rectal, muscle and pulmonary artery temperatures were decreased by 1.5 +/- 0.2, 0.8 +/- 0.1 and 1.0 +/- 0.2 degrees C, respectively (P < 0.05). Peak SR and the pattern of sweat ion losses during exercise was unchanged post training whereas SR and sweat losses during recovery were decreased (P < 0.05). Conclusions: Similar SRs for a given core temperature during exercise but a more rapid decrease in recovery resulted in an overall reduction in sweat fluid losses with no change in sweat ion losses after training. Relevance: The results provide insight into the extent to which short-term training can improve the capacity of horses to exercise in hot conditions.