Animal Science Unit, Gembloux Agro-Bio Tech, University of Liège, B-5030 Gembloux, Belgium.
J Dairy Sci. 2013 Mar;96(3):1844-55. doi: 10.3168/jds.2012-5947. Epub 2013 Jan 9.
This study was aimed to evaluate the degree of thermal stress exhibited by Holsteins under a continental temperate climate. Milk, fat, protein, and somatic cell count test-day records collected between 2000 and 2011 from 23,963 cows in 604 herds were combined with meteorological data from 14 public weather stations in Luxembourg. Daily values of 6 different thermal indices (TI) weighted in term of temperature, relative humidity, solar radiation, and wind speed were calculated by averaging hourly TI over 24h. Heat stress thresholds were first identified by a broken-line regression model. Regression models were thereafter applied to quantify milk production losses due to heat stress. The tipping points at which milk and protein yields declined were effectively identified. For fat yield, no valid threshold was identified for any of the studied TI. Daily fat yields tended to decrease steadily with increasing values of TI. Daily somatic cell score patterns were marked by increased values at both lowest and highest TI ranges, with a more pronounced reaction to cold stress for apparent temperature indices. Thresholds differed between TI and traits. For production traits, they ranged from 62 (TI(1)) to 80 (TI(3)) for temperature-humidity indices (THI) and from 16 (TI(5)) to 20 (TI(6)) for apparent temperature indices. Corresponding somatic cell score thresholds were higher and ranged from 66 (TI(1)) to 82 (TI(3)) and from 20 (TI(5)) to 23 (TI(6)), respectively. The largest milk decline per unit of mild, moderate, and extreme heat stress levels of 0.164, 0.356, and 0.955 kg, respectively, was observed when using the conventional THI (TI(1)). The highest yearly milk, fat, and protein losses of 54, 5.7, and 4.2 kg, respectively, were detected by TI(2), the THI index that is adjusted for wind speed and solar radiation. The latter index could be considered as the best indicator of heat stress to be used for forecast and herd management in a first step in temperate regions under anticipated climate changes.
本研究旨在评估荷斯坦奶牛在大陆温带气候下所承受的热应激程度。将 2000 年至 2011 年间 604 个牛群的 23963 头奶牛的产奶量、乳脂率、乳蛋白率和体细胞数测试日记录与来自卢森堡 14 个公共气象站的气象数据相结合。通过将 24 小时内每小时的热指数平均化，计算出 6 种不同热指数（TI）的日值，这些 TI 综合考虑了温度、相对湿度、太阳辐射和风速的权重。首先，通过折线回归模型确定热应激阈值。然后，应用回归模型来量化热应激对产奶量的损失。确定了牛奶和蛋白质产量下降的临界点。对于脂肪产量，在所研究的 TI 中，没有一个有效阈值。随着 TI 值的增加，脂肪日产量呈持续下降趋势。体细胞日评分模式的特点是在最低和最高 TI 范围内均呈升高趋势，而对于表观温度指数，冷应激的反应更为明显。阈值因 TI 和性状而异。对于生产性状，温度-湿度指数（THI）的范围从 62（TI(1)）到 80（TI(3)），而表观温度指数的范围从 16（TI(5)）到 20（TI(6)）。相应的体细胞评分阈值更高，范围从 66（TI(1)）到 82（TI(3)）和 20（TI(5)）到 23（TI(6)）。在使用传统 THI（TI(1)）时，分别观察到每单位轻度、中度和重度热应激水平下的牛奶产量下降 0.164、0.356 和 0.955kg。通过 TI(2)（一种调整了风速和太阳辐射的 THI 指数）检测到最高的年牛奶、脂肪和蛋白质损失分别为 54、5.7 和 4.2kg。该指数可以被认为是预测和牛群管理的最佳热应激指标，在预期气候变化下的温带地区可以作为第一步使用。
