Location: Forage-animal Production ResearchTitle: Regional differences in sweat rate response of steers to short-term heat stress) Author
Submitted to: Journal of Biometeorology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2008
Publication Date: 7/9/2008
Citation: Scharf, B., Was, L.E., Aiken, G.E., Spiers, D. 2008. Regional differences in sweat rate response of steers to short-term heat stress. Journal of Biometeorology. 52:725-732. Interpretive Summary: Rapid measurements of body temperatures in cattle are needed for scientific studies of body temperature responses to stressful environments. Rectal temperatures of cattle are often used as an indicator of thermal status, but also is the response with the greatest lag time. Skin temperature is generally more responsive than rectal temperature to changes in air temperature. Sweating of cattle also is important in thermoregulation. An experiment with steers compared relationships of sweating rate with rectal, skin, and air temperatures. Sweating rate was found to have its strongest relationship with air temperature. Sweating rate was more closely related with skin than with rectal temperatures; however, the strongest relationship was determined air temperature. It was concluded that thermal inputs other than rectal or skin temperatures drive the sweating response in cattle. This research provided stress physiologists with some insight into the sweating response of cattle, but further indicated the need for more research to determine the combination of thermal inputs that can drive sweating.
Technical 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 (Ta). cold chamber Ta was lowered to 8.4°C, while Ta 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 determinationof 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°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.