Geor R J, McCutcheon L J, Ecker G L, Lindinger M I
Department of Clinical Studies, Ontario Veterinary College, Guelph, Ontario N1G 2W1, Canada.
J Appl Physiol (1985). 2000 Dec;89(6):2283-93. doi: 10.1152/jappl.2000.89.6.2283.
The effect of humid heat acclimation on thermoregulatory responses to humid and dry exercise-heat stress was studied in six exercise-trained Thoroughbred horses. Horses were heat acclimated by performing moderate-intensity exercise for 21 days in heat and humidity (HH) [34.2-35.7 degrees C; 84-86% relative humidity (RH); wet bulb globe temperature (WBGT) index approximately 32 degrees C]. Horses completed exercise tests at 50% of peak O(2) uptake until a pulmonary arterial temperature (T(pa)) of 41.5 degrees C was attained in cool dry (CD) (20-21.5 degrees C; 45-50% RH; WBGT approximately 16 degrees C), hot dry (HD 0) [32-34 degrees C room temperature (RT); 45-55% RH; WBGT approximately 25 degrees C], and HH conditions (HH 0), and during the second hour of HH on days 3, 7, 14, and 21, and in HD on the 18th day (HD 18) of heat acclimation. The ratios of required evaporative capacity to maximal evaporative capacity of the environment (E(req)/E(max)) for CD, HD, and HH were approximately 1.2, 1.6, and 2.5, respectively. Preexercise T(pa) and rectal temperature were approximately 0.5 degrees C lower (P < 0. 05) on days 7, 14, and 21 compared with day 0. With exercise in HH, there was no effect of heat acclimation on the rate of rise in T(pa) (and therefore exercise duration) nor the rate of heat storage. In contrast, exercise duration was longer, rate of rise in T(pa) was significantly slower, and rate of heat storage was decreased on HD 18 compared with HD 0. It was concluded that, during uncompensable heat stress in horses, heat acclimation provided modest heat strain advantages when E(req)/E(max) was approximately 1.6, but at higher E(req)/E(max) no advantages were observed.
研究了湿热适应对6匹经过运动训练的纯种马在潮湿和干燥运动热应激下体温调节反应的影响。通过在高温高湿（HH）环境[34.2 - 35.7摄氏度；相对湿度（RH）84 - 86%；湿球黑球温度（WBGT）指数约32摄氏度]下进行21天的中等强度运动，使马匹适应热环境。马匹在凉爽干燥（CD）（20 - 21.5摄氏度；45 - 50% RH；WBGT约16摄氏度）、炎热干燥（HD 0）[室温（RT）32 - 34摄氏度；45 - 55% RH；WBGT约25摄氏度]和HH条件（HH 0）下，以峰值摄氧量的50%完成运动测试，直至肺动脉温度（T(pa)）达到41.5摄氏度，并在湿热适应的第3、7、14和21天的HH环境的第二个小时以及第18天的HD环境（HD 18）中进行测试。CD、HD和HH环境下所需蒸发能力与环境最大蒸发能力的比值（E(req)/E(max)）分别约为1.2、1.6和2.5。与第0天相比，第7、14和21天运动前的T(pa)和直肠温度约低0.5摄氏度（P < 0.05）。在HH环境中运动时，热适应对T(pa)的上升速率（以及运动持续时间）和热量储存速率均无影响。相比之下，与HD 0相比，HD 18时的运动持续时间更长，T(pa)的上升速率显著更慢，热量储存速率降低。得出的结论是，在马匹无法代偿的热应激期间，当E(req)/E(max)约为1.6时，热适应提供了适度的热应激优势，但在更高的E(req)/E(max)时未观察到优势。
