Heat storage in horses during submaximal exercise before and after humid heat acclimation

• Published in: Journal of applied physiology (1985) 2000-12, Vol.89 (6), p.2283-2293
• Main Authors: Geor, Raymond J, McCutcheon, Laura Jill, Ecker, Gayle L, Lindinger, Michael I
• Format: Article
• Language: English
• Subjects: Acclimatization - physiology; Animals; Biological and medical sciences; Body Temperature; Body Weight; Chronobiology; Environment; Exercise; Fundamental and applied biological sciences. Psychology; Heart Rate; Heat; Horses; Horses - physiology; Hot Temperature; Humidity; Motor Activity - physiology; Oxygen Consumption; Respiration; Stress; Sweating; Time Factors; Vertebrates: anatomy and physiology, studies on body, several organs or systems
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.2000.89.6.2283

Departments of 1  Clinical Studies and 2  Pathobiology, Ontario Veterinary College, and 3  Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario N1G 2W1, Canada 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°C; 84-86% relative humidity (RH); wet bulb globe temperature (WBGT) index ~32°C]. Horses completed exercise tests at 50% of peak O 2 uptake until a pulmonary arterial temperature (T pa ) of 41.5°C was attained in cool dry (CD) (20-21.5°C; 45-50% RH; WBGT ~16°C), hot dry (HD 0) [32-34°C room temperature (RT); 45-55% RH; WBGT ~25°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 ~1.2, 1.6, and 2.5, respectively. Preexercise T pa and rectal temperature were ~0.5°C lower ( P