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Body Temperature and Behavioral Activities of Four Breeds of Heifers in Shade and Full Sun

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

Citation:  Applied Engineering in Agriculture. 27(6): 999-1006. (doi: 10.13031/2013.40620) @2011
Authors:   K. G. Gebremedhin, C. N. Lee, P. E. Hillman, T. M. Brown-Brandl
Keywords:   Shade, Body temperature, Solar load, Hair-coat color, Heifers, Breed, Feedlot cattle

Four breeds of heifers, eight of each breed, were housed in two types of feedlot pens one with shade and the other with no shade (exposed to full sun). The breeds were: Black Angus, white Charolais, tan-colored MARC I, and dark-red colored MARC III. The objectives were to determine whether shade made a significant difference in thermal responses (animal activities and vaginal temperature) and to determine the effect of hair-coat color on body temperature due to solar exposure. Providing shade alleviated heat stress by lowering body temperature especially for black Angus and dark-red colored MARC III because of their higher hair-coat color capacity to absorb solar load. These two breeds spent more time standing in shade than the tan-colored MARC I and the white Charolais. The rate of increase of body temperature was higher when the heifers were lying down in full sun (0.61+0.27C/h) followed by lying down in shade (0.25+0.17C/h) because of reduced effective surface area to convective evaporative cooling (p<0.05). There was direct linear correlation (R2 0.90) between solar absorbing capacity of hair coat and percent of time the heifers spent in shade. The percent of time spent in shade both standing and lying down for each breed was: 89% for Black Angus, 81% for dark-red MARC III, 57% for tan-colored MARC I, and 55% for white Charolais. The study suggested that shade was critical for feedlot cows, especially those with dark hair coat, allowing them to thermally regulate their physiologic needs.

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