Regional differences in sweat rate response of steers to short-term heat stress |
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Authors: | B Scharf L E Wax G E Aiken D E Spiers |
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Institution: | (1) Department of Animal Science, University of Missouri, 920 East Campus Drive, Columbia, MO 65211, USA;(2) Forage-Animal Production Research Unit, USDA-ARS, Lexington, KY, USA |
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Abstract: | Six Angus steers (319 ± 8.5 kg) were assigned to one of two groups (hot or cold exposure) of three steers each, and placed
into two environmental chambers initially maintained at 16.5–18.8°C air temperature (T
a). Cold chamber T
a was lowered to 8.4°C, while T
a within the hot chamber was increased to 32.7°C over a 24-h time period. Measurements included respiration rate, and air and
body (rectal and skin) temperatures. Skin temperature was measured at shoulder and rump locations, with determination of sweat
rate using a calibrated moisture sensor. Rectal temperature did not change in cold or hot chambers. However, respiration rate
nearly doubled in the heat (P < 0.05), increasing when T
a was above 24°C. Skin temperatures at the two locations were highly correlated (P < 0.05) with each other and with T
a. In contrast, sweat rate showed differences at rump and shoulder sites. Sweat rate of the rump exhibited only a small increase
with T
a. However, sweat rate at the shoulder increased more than four-fold with increasing T
a. Increased sweat rate in this region is supported by an earlier report of a higher density of sweat glands in the shoulder
compared to rump regions. Sweat rate was correlated with several thermal measurements to determine the best predictor. Fourth-order
polynomial expressions of short-term rectal and skin temperature responses to hot and cold exposures produced r values of 0.60, 0.84, and 0.98, respectively. These results suggest that thermal inputs other than just rectal or skin temperature
drive the sweat response in cattle. |
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Keywords: | Cattle Sweat rate Heat Stress Acute |
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