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Title: Sweating rates of dairy and feedlot cows under stressful thermal environments

Author
item GEBREMEDHIN, K - CORNELL UNIVERSITY
item HILLMAN, P - CORNELL UNIVERSITY
item LEE, C - UNIV OF HAWAII
item COLLIER, R - UNIV OF ARIZONA
item WILLARD, S - MISSISSIPPI STATE UNIV
item ARTHINGTON, J - UNIV OF FLORIDA
item BROWN-BRANDL, TAMI

Submitted to: Livestock Environment International Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 8/19/2008
Publication Date: 12/1/2008
Citation: Gebremedhin, K.G., Hillman, P.E., Lee, C.N., Collier, R.J., Willard, S.T., Arthington, J.E., Brown Brandl, T.M. 2008. Sweating rates of dairy and feedlot cows under stressful thermal environments. In: Proceedings of Eighth International Livestock Environment Symposium,745-753. Iguassu Falls, Brazil.

Interpretive Summary: Hot weather causes heat stress in both beef cattle and dairy cattle. This heat stress results in losses in milk production and slower growth and in severe cases can cause death. As with humans, cattle sweat to stay cool in the summer. A study was conducted to determine sweating rates from several different breeds of cattle. The sweating rate of the cattle was influenced by coat color, wind speed, access to a shaded area, and breed.

Technical Abstract: Sweating rates from heat-stressed dairy and feedlot cows were measured using a portable calorimeter. Measurements were made when cows were in shade and exposed to direct sunlight (120 to 1100 W/m2) under different air velocities (0.1 to 1.8 m/s). The effect of color of hair coat (black and white) on sweating rate was compared. The beef cows were of three genetic strain (Brookville black, Kansas black and White) Angus. Sweating rate of the Holstein cows at zero air velocity was 62 g/h-m2, and at 0.2 and 1.0 m/s was 238 and 333 g/h-m2, respectively, when ambient temperature was 33 °C , relative humidity was 52% and solar load was 740 W/m2. The sweating rate of the white Angus was 310 g/m2-h compared to 177 g/m2-h and 202 g/m2-h for the Brookville and Kansas Angus, respectively. The dorsal hair coat temperature of the Angus with black hair coat increased 1.2°C per 100 W/m2 increase in solar load, while the white Angus only increased about 0.1°C per 100 W/m2 increase in solar load. The white Angus had a 0.8 to 1.7°C lower body temperature than the black Angus. Kansas black, the genetic strain of black Angus from northern climates had a 0.9°C higher body temperature than Brookville black, the genetic strain from Florida. Although sweating rates of the two black strains of Angus were similar, the sweating rate of the Kansas strain was more erratic than the Brookville strain, suggesting that Kansas strain could not maintain a steady sweating rate under similar heat stress conditions.