Mader T L, Davis M S, Brown-Brandl T
University of Nebraska, Concord, 68728, USA.
J Anim Sci. 2006 Mar;84(3):712-9. doi: 10.2527/2006.843712x.
Data from 3 summer feedlot studies were utilized to determine the environmental factors that influence heat stress in cattle and also to determine wind speed (WSPD; m.s(-1)) and solar radiation (RAD; W.m(-2)) adjustments to the temperature-humidity index (THI). Visual assessments of heat stress, based on panting scores (0 = no panting to 4 = severe panting), were collected from 1400 to 1700. Mean daily WSPD, black globe temperature at 1500, and minimums for nighttime WSPD, nighttime black globe 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 to equal -7.563 + (0.121 x THI) - (0.241 x WSPD) + (0.00082 x RAD) (R2 = 0.49). Using the ratio of WSPD to THI and RAD to THI (- 1.992 and 0.0068 for WSPD and RAD, respectively), adjustments to the THI were derived for WSPD and RAD. On the basis of these ratios and the average hourly data for 1400 to 1700, the THI, adjusted for WSPD and RAD, equals [4.51 + THI - (1.992 x WSPD) + (0.0068 x RAD)]. Four separate cattle studies, comparable in size, type of cattle, and number of observations to the 3 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 4 studies were 1.22, 0.94, 1.32, and 2.00 vs. the predicted panting scores of 1.15, 1.17, 1.30, and 1.96, respectively. Correlations between THI and panting score in these studies ranged from r = 0.47 to 0.87. Correlations between the adjusted THI and mean panting score ranged from r = 0.64 to 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 black globe 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.
利用3项夏季饲养场研究的数据来确定影响牛热应激的环境因素，并确定风速（WSPD；米/秒）和太阳辐射（RAD；瓦/平方米）对温湿度指数（THI）的调整。基于喘气评分（0 = 不喘气至4 = 严重喘气）对热应激进行视觉评估，评估时间为1400至1700。发现平均每日风速、1500时的黑球温度以及夜间风速最小值、夜间黑球THI和每日相对湿度对1400至1700时的喘气评分影响最大（R2 = 0.61）。根据THI、WSPD和RAD的每小时值，确定喘气评分等于 -7.563 +（0.121×THI）-（0.241×WSPD）+（0.00082×RAD）（R2 = 0.49）。利用WSPD与THI的比值以及RAD与THI的比值（WSPD和RAD分别为 -1.992和0.0068），得出WSPD和RAD对THI的调整值。基于这些比值以及1400至1700时的平均每小时数据，经WSPD和RAD调整后的THI等于[4.51 + THI -（1.992×WSPD）+（0.0068×RAD）]。利用4项单独的牛研究（在规模、牛的类型和观察数量方面与3项原始研究相当）来评估经WSPD和RAD调整后的THI方程的准确性，以及调整后的THI与喘气评分之间的关系。在这4项研究中，对黑色皮毛牛个体观察得出的平均喘气评分分别为1.22、0.94、1.32和2.00，而预测的喘气评分分别为1.15、1.17、1.30和1.96。这些研究中THI与喘气评分之间的相关性范围为r = 0.47至0.87。调整后的THI与平均喘气评分之间的相关性范围为r = 0.64至0.80。这些调整在一天内使用每小时数据或当前条件来预测下午时段的THI时最为适用。除了下午的情况外，夜间条件，包括最小风速、最小黑球THI和最小THI，也被发现会影响牛所经历的热应激。虽然仅了解THI有助于确定热应激的可能性，但对THI进行风速和太阳辐射调整能更准确地评估动物的不适程度。
