The effects of heat stress in Italian Holstein dairy cattle
The effects of heat stress in Italian Holstein dairy cattle
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DOI：
10.3168/jds.2013-6611
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发表时间：
2014-01-01
影响因子：
3.5
通讯作者：
Nardone, A.
中科院分区：
文献类型：
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作者：
Bernabucci, U.;Biffani, S.;Nardone, A.
本研究的数据集包括来自 484 个农场的 191,012 头、二胎和三胎荷斯坦奶牛的 1,488,474 条测试日记录，记录了牛奶、脂肪和蛋白质产量以及脂肪和蛋白质百分比。数据收集自 2001 年至 2007 年，并与 35 个气象站的气象数据合并。使用线性模型（M1）来估计温湿度指数（Till）对生产性状的影响。 M1 的最小二乘均值用于通过两相线性回归程序 (M2) 检测所有胎次的产奶量 Till 阈值。使用多性状重复性测试模型（M3）来估计所有性状的方差分量，并定义虚拟回归变量（t）来估计热应激引起的产量下降。此外，估计方差分量和 M3 用于估计第 1 胎次的产奶量和蛋白质百分比的传统和耐热育种值（估计育种值，EBV）。数据分析 (M2) 表明，3 胎次和性状的产奶量开始下降的每日 Till 范围为 65 至 76。这些 Till 值可以通过不同的温度/湿度组合来实现，温度范围为 21 至 36 °C 和相对湿度值从 5% 到 95%。对于所有性状，在测试日前 4 天观察到 Till 对 3 胎次的负面影响最高。 Till 对生产性状的负面影响表明，初产奶牛对热应激的敏感度低于多产奶牛。与胎次相比，蛋白质含量的一般加性遗传方差减少，产奶量、脂肪和蛋白质产量的一般加性遗传方差增加。耐热性的加性遗传方差显示，从第一胎到第三胎，牛奶、蛋白质和脂肪产量以及蛋白质百分比有所增加。一般效应和热应激效应之间的遗传相关性都是不利的（从-0.24到-0.56）。计算每头奶牛和公牛每个性状的三个 EBV（传统 EBV、包含 Till 协变量效应估计的传统 EBV 和耐热性 EBV），并比较 1985 年以后出生的 283 头至少有 50 个女儿的公牛的 EBV 排名。当模型中包含蒂尔时，17 头和 32 头公牛的产奶量和蛋白质百分比的排名分别发生了变化。耐热性遗传成分不可忽视，表明耐热性选择应纳入选择目标。
The data set for this study comprised 1,488,474 test-day records for milk, fat, and protein yields and fat and protein percentages from 191,012 first-, second-, and third-parity Holstein cows from 484 farms. Data were collected from 2001 through 2007 and merged with meteorological data from 35 weather stations. A linear model (M1) was used to estimate the effects of the temperature-humidity index (Till) on production traits. Least squares means from M1 were used to detect the Till thresholds for milk production in all parities by using a 2-phase linear regression procedure (M2). A multiple-trait repeatability test-model (M3) was used to estimate variance components for all traits and a dummy regression variable (t) was defined to estimate the production decline caused by heat stress. Additionally, the estimated variance components and M3 were used to estimate traditional and heat-tolerance breeding values (estimated breeding values, EBV) for milk yield and protein percentages at parity 1. An analysis of data (M2) indicated that the daily Till at which milk production started to decline for the 3 parities and traits ranged from 65 to 76. These Till values can be achieved with different temperature/humidity combinations with a range of temperatures from 21 to 36 C and relative humidity values from 5 to 95%. The highest negative effect of Till was observed 4 d before test day over the 3 parities for all traits. The negative effect of Till on production traits indicates that first-parity cows are less sensitive to heat stress than multiparous cows. Over the parities, the general additive genetic variance decreased for protein content and increased for milk yield and fat and protein yield. Additive genetic variance for heat tolerance showed an increase from the first to third parity for milk, protein, and fat yield, and for protein percentage. Genetic correlations between general and heat stress effects were all unfavorable (from -0.24 to -0.56). Three EBV per trait were calculated for each cow and bull (traditional EBV, traditional EBV estimated with the inclusion of Till covariate effect, and heat tolerance EBV) and the rankings of EBV for 283 bulls born after 1985 with at least 50 daughters were compared. When Till was included in the model, the ranking for 17 and 32 bulls changed for milk yield and protein percentage, respectively. The heat tolerance genetic component is not negligible, suggesting that heat tolerance selection should be included in the selection objectives.