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Sweating Rates of Dairy Cows and Beef Heifers in Hot Conditions

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Transactions of the ASABE. 51(6): 2167-2178. (doi: 10.13031/2013.25397) @2008
Authors:   K. G. Gebremedhin, P. E. Hillman, C. N. Lee, R. J. Collier, S. T. Willard, J. D. Arthington, T. M. Brown-Brandl
Keywords:   Air temperature, Air velocity, Beef heifers, Breed, Dairy cows, Evaporative cooling, Hair-coat color, Heat stress, Relative humidity, Solar load

Sweating rates from heat-stressed dairy cows and beef heifers 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 cows and beef heifers, and determine the level of influence of environmental factors (air temperature, relative humidity, solar load, and 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 38.8C (threshold for heat stress). Sweating rates ranged between 189 84.6 and 522 127.7 g/m2-h. Body temperature ranged between 39.3 0.53C and 41.7 0.19C. Differences in sweating rates were statistically significant at P < 0.05 between breeds, between black and white hair coats, and changes in solar load, relative humidity, and air velocity. Wetting the skin surface and increasing air velocity profoundly increased evaporation rate by converting sensible heat to latent heat.

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