Department of Animal Breeding, University of Kassel, 37213 Witzenhausen, Germany.
J Dairy Sci. 2011 Aug;94(8):4129-39. doi: 10.3168/jds.2010-4063.
Data used in the present study included 1,095,980 first-lactation test-day records for protein yield of 154,880 Holstein cows housed on 196 large-scale dairy farms in Germany. Data were recorded between 2002 and 2009 and merged with meteorological data from public weather stations. The maximum distance between each farm and its corresponding weather station was 50 km. Hourly temperature-humidity indexes (THI) were calculated using the mean of hourly measurements of dry bulb temperature and relative humidity. On the phenotypic scale, an increase in THI was generally associated with a decrease in daily protein yield. For genetic analyses, a random regression model was applied using time-dependent (d in milk, DIM) and THI-dependent covariates. Additive genetic and permanent environmental effects were fitted with this random regression model and Legendre polynomials of order 3 for DIM and THI. In addition, the fixed curve was modeled with Legendre polynomials of order 3. Heterogeneous residuals were fitted by dividing DIM into 5 classes, and by dividing THI into 4 classes, resulting in 20 different classes. Additive genetic variances for daily protein yield decreased with increasing degrees of heat stress and were lowest at the beginning of lactation and at extreme THI. Due to higher additive genetic variances, slightly higher permanent environment variances, and similar residual variances, heritabilities were highest for low THI in combination with DIM at the end of lactation. Genetic correlations among individual values for THI were generally >0.90. These trends from the complex random regression model were verified by applying relatively simple bivariate animal models for protein yield measured in 2 THI environments; that is, defining a THI value of 60 as a threshold. These high correlations indicate the absence of any substantial genotype × environment interaction for protein yield. However, heritabilities and additive genetic variances from the random regression model tended to be slightly higher in the THI range corresponding to cows' comfort zone. Selecting such superior environments for progeny testing can contribute to an accurate genetic differentiation among selection candidates.
本研究的数据包括德国 196 个大型奶牛场的 154880 头荷斯坦奶牛的 1095980 个泌乳期第一次产奶测试日记录。数据记录于 2002 年至 2009 年，与公共气象站的气象数据合并。每个农场与其相应气象站之间的最大距离为 50 公里。每小时温湿度指数（THI）通过平均每小时测量的干球温度和相对湿度计算得出。在表型尺度上，THI 的增加通常与日蛋白产量的减少相关。在遗传分析中，使用随时间变化的（泌乳天数，DIM）和 THI 相关的协变量的随机回归模型。加性遗传和永久环境效应与该随机回归模型和阶数为 3 的勒让德多项式拟合。此外，固定曲线也用阶数为 3 的勒让德多项式拟合。通过将 DIM 分为 5 类，将 THI 分为 4 类，得到 20 个不同的类，然后拟合异质残差。日蛋白产量的加性遗传方差随热应激程度的增加而降低，在泌乳初期和极端 THI 时最低。由于加性遗传方差较高，永久环境方差略高，且残差方差相似，因此在泌乳末期低 THI 与 DIM 结合时，遗传力最高。THI 个体值之间的遗传相关系数通常>0.90。通过在 2 个 THI 环境下测量蛋白质产量，应用相对简单的二元动物模型验证了该复杂随机回归模型的这些趋势，即定义 THI 值为 60 作为阈值。这些高相关性表明，蛋白质产量不存在任何实质性的基因型×环境互作。然而，随机回归模型中的遗传力和加性遗传方差在奶牛舒适区对应的 THI 范围内略高。在选择这样的优良环境进行后裔测试，可以有助于在选择候选者之间进行准确的遗传分化。
