|Brown Brandl, Tami|
Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2008
Publication Date: 12/31/2008
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 cows and beef heifers in hot conditions. Transactions ASABE 51(6):2167-2178. 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” and a “Bovine Evaporation Meter” designed and fabricated for the studies reported herein. Measurements were taken when cows were in their natural habitat. The focus of the study was to compare sweating rates measured from different breeds of dairy and feedlot cows, and determine the level of influence of environmental factors (air temperature, relative humidity, solar load , air velocity), and hair-coat color on sweating rate. The cows were exposed to solar radiation greater than 500 W/m2 (average 833 ± 132 W/m2), average THI was 82.7 ± 1.64 for all studies except for the Nebraska data where the THI was 77.4 ± 4. Air velocity in the sample area was between 0.8 and 1.2 m/s, and body (rectal) temperature was greater than 38.8°C (threshold for heat stress). Sweating rates ranged between 189 ± 84.6 and 522 ± 127.7 g/m2-h. Body temperature ranged between 39.3 ± 0.53 and 41.7 ± 0.19 °C. Differences in sweating rates were statistically significant at P <0.05 value between breeds, between black and white hair coats, and changes in solar load, relative humidity, and air velocity. Wetting the skin surface coupled with increased air velocity profoundly increased evaporation rate by converting sensible heat to latent heat.