Equine sweating responses to submaximal exercise during 21 days of heat acclimation.
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 degrees C, 80-85% relative humidity). On days 0, 3, 7, 14, and 21, horses completed a standardized exercise test on a treadmill (6 degrees incline) at a speed eliciting 50% of maximal O(2) uptake until a pulmonary artery temperature of 41.5 degrees 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 degrees 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 approximately 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 ( approximately 1 degrees 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.
McCutcheon
L J
LJ
Department of Pathobiology, Ontario Veterinary College, Guelph, Ontario, Canada N1G 2W1.
Geor
R J
RJ
Ecker
G L
GL
Lindinger
M I
MI
D000064:Acclimatization / Q000502:physiology*; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D001835:Body Weight / Q000502:physiology; D006736:Horses / Q000502:physiology*; D006358:Hot Temperature / Q000009:adverse effects*; D006813:Humidity; D010805:Physical Conditioning, Animal / Q000502:physiology; D005082:Physical Exertion / Q000502:physiology*; D012420:Running / Q000502:physiology; D012964:Sodium / Q000032:analysis / Q000378:metabolism; D013542:Sweat / Q000737:chemistry / Q000378:metabolism; D013546:Sweating / Q000502:physiology*; D013997:Time Factors; D014882:Water-Electrolyte Balance / Q000502:physiology
D012964:Sodium