Bernabucci U, Biffani S, Buggiotti L, Vitali A, Lacetera N, Nardone A
Dipartimento di scienze e tecnologie per l'Agricoltura, le Foreste, la Natura e l'Energia (DAFNE), Università degli Studi della Tuscia, 01100 Viterbo, Italy.
Associazione Nazionale Allevatori Frisona Italiana (ANAFI), 26100 Cremona, Italy.
J Dairy Sci. 2014;97(1):471-86. doi: 10.3168/jds.2013-6611. Epub 2013 Nov 7.
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 (THI) on production traits. Least squares means from M1 were used to detect the THI 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 THI at which milk production started to decline for the 3 parities and traits ranged from 65 to 76. These THI 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 THI was observed 4 d before test day over the 3 parities for all traits. The negative effect of THI 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 THI 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 THI 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.
本研究的数据集包含来自484个农场的191,012头头胎、二胎和三胎荷斯坦奶牛的1,488,474条测试日记录，涉及牛奶、脂肪和蛋白质产量以及脂肪和蛋白质百分比。数据收集于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）来估计温度湿度指数（THI）对生产性状的影响。通过两阶段线性回归程序（M2），利用M1的最小二乘均值来检测所有胎次牛奶生产的THI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成分，并定义一个虚拟回归变量（t）来估计热应激导致的产量下降。此外，利用估计的方差成分和M3来估计头胎时牛奶产量和蛋白质百分比的传统育种值和耐热育种值（估计育种值，EBV）。数据分析（M2）表明，三个胎次和性状的牛奶产量开始下降时的每日THI范围为65至76。这些THI值可以通过不同的温度/湿度组合实现，温度范围为21至36°C，相对湿度值为5至95%。在所有性状的三个胎次中，在测试日前4天观察到THI的最高负面影响。THI对生产性状的负面影响表明，头胎奶牛比多胎奶牛对热应激的敏感性更低。在不同胎次中，蛋白质含量的一般加性遗传方差下降，而牛奶产量、脂肪和蛋白质产量的加性遗传方差增加。牛奶、蛋白质和脂肪产量以及蛋白质百分比的耐热加性遗传方差从第一胎到第三胎呈增加趋势。一般和热应激效应之间的遗传相关性均为不利（从-0.24至-0.56）。为每头母牛和公牛计算了每个性状的三个EBV（传统EBV、包含THI协变量效应估计的传统EBV和耐热EBV），并比较了1985年后出生且至少有50个女儿的283头公牛的EBV排名。当模型中包含THI时，牛奶产量和蛋白质百分比的排名分别有17头和32头公牛发生了变化。耐热遗传成分不可忽略，这表明耐热性选择应纳入选择目标。
