|Brown Brandl, Tami|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/1/2005
Publication Date: 2/1/2006
Citation: Mader, T.L., Davis, M.S., Brown Brandl, T.M. 2006. Environmental factors influencing heat stress in feedlot cattle. Journal Animal Science. 84:712-719. Interpretive Summary: Environmental conditions including temperature, humidity, wind speed, and solar radiation all affect the sensation of heat and the discomfort level of animals. An equation developed in 1959 has been used by the cattle industry to determine the level of discomfort due to the heat. However, this equation does not include the factors of wind speed or solar radiation. Data from several studies provided a basis of including adjustments for wind speed and solar radiation.
Technical Abstract: Data from three summer feedlot studies were utilized to determine environmental factors which influence cattle heat stress and determine wind speed (WSPD, m/s) and solar radiation (RAD, kcal/m2) adjustments to the temperature-humidity index (THI). Visual assessments of heat stress, based on panting scores (0 = no panting, 4 = severe panting), were collected from 1400 to 1700. Mean daily WSPD, 1500 blackglobe temperature, and minimums for nighttime time WSPD, nighttime blackglobe THI, and daily relative humidity were found to have the greatest influence on panting score from 1400 to 1700 (R2 = 0.61). From hourly values for THI, WSPD, and RAD, panting score was determined (R2 = 0.49) to equal -7.563 + (0.121 * THI) – (0.241 * WSPD) + (0.00095 * RAD). Using the ratio of WSPD to THI and RAD to THI (-1.992 and 0.0079 for WSPD and RAD, respectively) adjustments to the THI were derived for WSPD and RAD. On the basis of these ratios and average 1400 to 1700 hourly data, the THI, adjusted for WSPD and RAD, equals [4.51 + THI – (1.992*WSPD) + (0.0079*RAD)]. Four separate cattle studies, comparable in size, type of cattle, and number of observations to the three original studies, were utilized to evaluate the accuracy of the THI equation adjusted for WSPD and RAD, and the relationship between the adjusted THI and panting score. Mean panting score, derived from individual observations of black hided cattle, in these four studies were 1.22, 0.94, 1.32, and 2.00 versus the predicted panting scores of 1.15, 1.17, 1.30, and 1.96, respectively. Correlation coefficients between THI and panting score in these studies ranged from 0.47 to 0.87. Correlation coefficients between the adjusted THI and mean panting score ranged from 0.64 and 0.80. These adjustments would be most appropriate to use, within a day, to predict THI during the afternoon hours using hourly data or current conditions. In addition to afternoon conditions, nighttime conditions, including minimum WSPD, minimum blackglobe THI, and minimum THI were also found to influence heat stress experienced by cattle. Although knowledge of THI alone is beneficial in determining the potential for heat stress, WSPD and RAD adjustments to the THI more accurately assess animal discomfort.