Is the temperature-humidity index the best indicator of heat stress in lactating dairy cows in a subtropical environment?
Is the temperature-humidity index the best indicator of heat stress in lactating dairy cows in a subtropical environment?
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DOI：
10.3168/jds.2008-1370
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发表时间：
2009-01-01
影响因子：
3.5
通讯作者：
Hansen, P. J.
中科院分区：
文献类型：
--
作者：
Dikmen, S.;Hansen, P. J.
几种温度-湿度指数（THI）已被用来估计奶牛所经历的热应激程度。目前的目标是使用气象变量开发方程来预测亚热带环境中泌乳奶牛的直肠温度，并将这些方程与使用 8 个不同 THI 的方程的拟合优度进行比较。 8 月至 12 月期间，对佛罗里达州中北部 1,280 头泌乳荷斯坦奶牛进行了 1500 至 1700 小时的直肠温度测量。奶牛所在谷仓记录的气象数据包括干球温度（Tdb）、相对湿度（RH）、露点温度和风速。计算湿球温度。在第一个系列的分析中，回归分析用于使用气象变量和 THI 来模拟直肠温度。使用 Tdb 的 r(2) (0.41) 略小于使用除一个 THI 之外的所有模型的模型（r(2) 在 0.42 和 0.43 之间）。使用 Tdb 的方程的 r(2) 可以通过在模型中添加 RH (r(2) = 0.43) 或 RH 和 RH2 (r(2) = 0.44) 来改进。在第二次分析中，使用前向选择、后向消除和逐步选择程序对气象变量进行回归分析。所有模型都给出相似的拟合优度 (r(2) = 0.44)。以直肠温度作为类别变量进行方差分析，以确定与高热相关的气象测量的最小二乘均值。 29.7 摄氏度的 Tdb 与 39 摄氏度的直肠温度相关，31.4 摄氏度的 Tdb 与 39.5 摄氏度的直肠温度相关。总之，Tdb 几乎与 THI 一样好，可以预测亚热带环境中哺乳期荷斯坦牛的直肠温度。与特定直肠温度相关的气象变量值的估计对于将环境条件与热应激奶牛经历的高热程度联系起来应该是有价值的。
Several temperature-humidity indexes (THI) have been used to estimate the degree of thermal stress experienced by dairy cows. The present objectives were to develop equations using meteorological variables that predicted rectal temperature of lactating cows in a subtropical environment and compare the goodness of fit of these equations to those using 8 different THI. Rectal temperature was measured between 1500 and 1700 h in 1,280 lactating Holstein cows in north central Florida between August and December. Meteorological data recorded in the barn where cows were located included dry bulb temperature (Tdb), relative humidity (RH), dew point temperature, and wind speed. Wet bulb temperature was calculated. In the first series of analyses, regression analysis was used to model rectal temperature using the meteorological variables as well as THI. The r(2) using Tdb (0.41) was slightly less than for models using all but one THI (r(2) between 0.42 and 0.43). The r(2) for equations using Tdb could be improved by adding RH (r(2) = 0.43) or RH and RH2 (r(2) = 0.44) to the model. In the second analysis, regression analysis was performed using forward selection, backward elimination, and stepwise selection procedures with the meteorological variables. All models gave a similar goodness of fit (r(2) = 0.44). An analysis of variance with rectal temperature as a class variable was performed to determine the least squares means of meteorological measurements associated with hyperthermia. A Tdb of 29.7 degrees C was associated with rectal temperature of 39 degrees C, and a Tdb of 31.4 degrees C was associated with rectal temperature of 39.5 degrees C. In conclusion, Tdb is nearly as good a predictor of rectal temperatures of lactating Holsteins in a subtropical environment as THI. Estimates of values of meteorological variables associated with specific rectal temperatures should prove valuable in relating environmental conditions to the magnitude of hyperthermia experienced by heat-stressed cows.