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

Citation:  Proceedings of the Seventh International Symposium, 18-20 May 2005 (Beijing, China) Publication Date 18 May 2005  701P0205.(doi:10.13031/2013.18360)
Authors:   P.E. Hillman, K.G. Gebremedhin, T.M. Brown-Brandl, and C.N. Lee
Keywords:   Thermoregulation, behavior, shade, beef heifers, feedlot, heat stress, solar load

Behavioral activities of 32 heifers in pens with shade and no shade (sunlight) were observed to establish whether or not providing shade made a difference in recorded vaginal temperatures of heifers. Four breeds of heifers, 8 of each breed: black Angus, white Charolais, tan-colored MARC I and dark red MARC III were used in order to establish the effect of hair coat color on thermal response. A mechanistic heat and mass transfer model that uses environmental parameters and physical and optical properties of hair and hair coat as input was used to do thermal analysis. There was no significant difference in measured internal body temperature between breeds for heifers in shade or sunlight at ambient temperature of 36C. Hair color played a significant role in solar radiation absorption. Cows with black and dark red colors absorbed high solar radiation than heifers with white and tan. The model predicted a benefit in providing shade when ambient air temperature was 36C. A benefit was not apparent when air temperature was 42C. The model predicted that sensible heat load was sensitive to ambient air temperature, air velocity and density of hair coat.

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