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Physiological Responses of Dairy Cows during Extended Solar Exposure

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

Citation:  2010 Pittsburgh, Pennsylvania, June 20 - June 23, 2010  1009532.(doi:10.13031/2013.29927)
Authors:   Kifle G Gebremedhin, Chin N Lee, Peter E Hillman, Robert J Collier
Keywords:   Dairy cows, Heat stress, Sweating rate, Respiration rate, Core temperature, Skin temperature

Sweating and respiration rates, and skin (dorsal) and core (rectal) temperatures of 12 Holstein dairy cows were measured in controlled environments at the William Parker Agricultural Research Complex, University of Arizona-Tucson. The focus of the study was: (1) to establish the pattern (linear or periodic) of sweating, (2) to establish whether skin or core temperature drives sweating, (3) to determine how cows react to a prolonged solar exposure, and (4) to compare dairy cows physiological responses to hot and humid versus hot and dry environmental conditions. The cows were divided into two groups of 6 cows each and were housed alternately between two chambers. The two chambers were identical but one (experimental chamber) included solar lamps to simulate solar load. The cows were alternately exposed to 550 W/m2 solar load, THI was initially set at 83 and later at 79.6, and air velocity in the measurement area on the dorsal surface was between 0.8 and 1.2 m/s. Skin temperature was greater than 35C (threshold for heat stress). There was considerable variation in sweating rates between cows of the Holstein breed. Cows sweat in a cyclic manner and the results suggest that skin temperature is the primary driving force for sweating. The maximum sweating rate of dairy cows and feedlot heifers is around 660 g/m2-h. A prolonged exposure to hot and dry environmental condition made entirely black or predominantly black cows to foam in the mouth, stick their tongues out, and drool, and immediate intervention with water spraying helped to alleviate the thermal stress.

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