|Brown Brandl, Tami|
Submitted to: Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/14/2005
Publication Date: 5/16/2005
Citation: Hillman, P.E., Gebremedhin, K.G., Brown Brandl, T.M., Lee, C.N. 2005. Thermal analysis and behavioral activity of heifers in shade or sunlight. Proceedings, Seventh International Livestock Environmental Symposium. p. 151-161. Interpretive Summary: A study was conducted to determine the effect of providing shade for the well-being of different breeds of cattle. The experiment used 32 cattle of four breeds. Body temperature and activity were observed over a two-week period. Hair density and diameter were measured, as well as reflectivity. The breeds were black Angus, white Charolais, a tan-colored crossbred, and a dark-red crossbred. The heat and mass transfer model used inputs of weather, and measured properties of the hair. Based on model predictions and experiment outcome – there was no effect of shade or sunlight on body temperature. However, cattle with dark hair coats absorbed more heat from the sun than those with light hair coats. Body temperature was not affected because this gain was offset by a greater evaporative heat loss. Shade only provided a modest benefit to cattle with dark hair coats at 42C, and no benefit to light colored cattle. A more important factor than shade was to reduce hair density, which partially explains why animals shed thick winter hair coats.
Technical Abstract: 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. Heifers with black and dark-red colors absorbed higher solar radiation than heifers with white and tan. The model predicted a benefit in providing shade when ambient air temperature was 42C. A benefit was not apparent when air temperature was 36C. The model predicted that sensible heat load was sensitive to ambient air temperature, air velocity, and density of hair coat.