|Brown Brandl, Tami|
Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2011
Publication Date: 11/1/2011
Citation: Gebremedhin, K.G., Lee, C.N., Hillman, P.E., Brown Brandl, T.M. 2011. Body temperature and behavioral activities of four breeds of heifers in shade and full sun. Applied Engineering in Agriculture. 27(6):999-1006. Interpretive Summary: The impacts of hot weather on cattle production are varied, ranging from little to no effect from a brief exposure, to death of vulnerable animals during an extreme heat event. Shade has been shown to reduce heat stress on feedlot cattle. In this study, we investigated the effects of shade on the body temperature and animal behavior in cattle of four different breeds with differing coat colors. We determined that shade alleviated heat stress by lowering body temperature. We observed a larger impact on the cattle with the black and dark-red coat colors, as the darker coat colors absorb more solar load than the lighter colored coats. The dark colored cattle spent more time in the shade.
Technical Abstract: Heifers from four breeds, 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, Charolais (white), MARC I (tan) and MARC III (dark red). The objectives were to determine whether shade made a significant difference in thermal responses (animal activities and vaginal temperature) and the effect of hair-coat color on body temperature due to solar exposure. Providing shade alleviated heat stress by lowering body temperature, especially for the Black Angus and dark-red 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 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 +/ 0.27 deg C/hr), followed by lying down in shade (0.25 +/ 0.17 deg C/hr) because of reduced effective surface area to convective evaporative cooling. There was direct linear correlation (R**2 approximately 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 MARC I and 55% for white Charolais.