Regional differences in sweat rate response of steers to short-term heat stress.
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 degrees C air temperature (Ta). Cold chamber Ta was lowered to 8.4 degrees C, while Ta within the hot chamber was increased to 32.7 degrees 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 Ta was above 24 degrees C. Skin temperatures at the two locations were highly correlated (P < 0.05) with each other and with Ta. In contrast, sweat rate showed differences at rump and shoulder sites. Sweat rate of the rump exhibited only a small increase with Ta. However, sweat rate at the shoulder increased more than four-fold with increasing Ta. 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.
Scharf
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B
Department of Animal Science, University of Missouri, 920 East Campus Drive, Columbia, MO 65211, USA.
Wax
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LE
Aiken
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GE
Spiers
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DE
D000818:Animals; D002369:Castration; D002417:Cattle / Q000502:physiology*; D003198:Computer Simulation; D004777:Environment; D018869:Heat-Shock Response / Q000502:physiology*; D006358:Hot Temperature; D008297:Male; D008954:Models, Biological; D012881:Skin Temperature / Q000502:physiology*; D013546:Sweating / Q000502:physiology*; D013997:Time Factors