Equine sweating responses to submaximal exercise during 21 days of heat acclimation

• Published in: Journal of applied physiology (1985) 1999-11, Vol.87 (5), p.1843-1851
• Main Authors: McCutcheon, Laura Jill, Geor, Raymond J, Ecker, Gayle L, Lindinger, Michael I
• Format: Article
• Language: English
• Subjects: Acclimatization - physiology; Anatomy & physiology; Animals; Biological and medical sciences; Body fluids; Body Temperature - physiology; Body Weight - physiology; Exercise; Fundamental and applied biological sciences. Psychology; Heat; Horses; Horses - physiology; Hot Temperature - adverse effects; Humidity; Physical Conditioning, Animal - physiology; Physical Exertion - physiology; Running - physiology; Sodium - analysis; Sodium - metabolism; Sweat - chemistry; Sweat - metabolism; Sweating - physiology; Thermoregulation. Hibernation. Estivation. Ecophysiology and environmental effects; Time Factors; Vertebrates: anatomy and physiology, studies on body, several organs or systems; Water-Electrolyte Balance - physiology
• ISSN: 8750-7587; 1522-1601
• DOI: 10.1152/jappl.1999.87.5.1843

Departments of 1  Pathobiology and 2  Clinical Studies, Ontario Veterinary College, and 3  Department of Human Biology and Nutritional Sciences, University of Guelph, Guelph, Ontario, Canada N1G 2W1 This study examined sweating responses in six exercise-trained horses during 21 consecutive days (4 h/day) of exposure to, and daily exercise in, hot humid conditions (32-34°C, 80-85% relative humidity). On days 0, 3, 7, 14 , and 21 , horses completed a standardized exercise test on a treadmill (6° incline) at a speed eliciting 50% of maximal O 2 uptake until a pulmonary artery temperature of 41.5°C was attained. Sweat was collected at rest, every 5 min during exercise, and during 1 h of standing recovery for measurement of ion composition (Na + , K + , and Cl ) and sweating rate (SR). There was no change in the mean time to reach a pulmonary artery temperature of 41.5°C (range 19.09   ± 1.41 min on day 0  to 20.92 ± 1.98 min on day 3 ). Peak SR during exercise (ml · m 2 · min 1 ) increased on day 7  (57.5 ± 5.0) but was not different on day 21  (48.0 ± 4.7) compared with day 0  (52.0 ± 3.4). Heat acclimation resulted in a 17% decline in SR during recovery and decreases in body mass and sweat fluid losses during the standardized exercise test of 25 and 22%, respectively, by day 21 . By day 21 , there was also a 10% decrease in mean sweat Na + concentration for a given SR during exercise and recovery; this contributed to an ~26% decrease in calculated total sweat ion losses (3,112 ± 114 mmol on day 0  vs. 2,295 ± 107 mmol on day 21 ). By day 21 , there was a decrease in sweating threshold (~1°C) but no change in sweat sensitivity. It is concluded that horses responded to 21 days of acclimation to, and exercise in, hot humid conditions with a reduction in sweat ion losses attributed to decreases in sweat Na + concentration and SR during recovery. incompensable heat stress; thermoregulation; sweat; sodium; potassium; chloride