Department of Genetics, University of Córdoba, Córdoba, Spain.
J Anim Breed Genet. 2012 Aug;129(4):306-15. doi: 10.1111/j.1439-0388.2011.00984.x. Epub 2012 Jan 3.
Monthly test-day records of milk yield and composition in Murciano-Granadina (MG) and Payoya (PYA) dairy goats were combined with weather data from meteorological stations, to analyse the effects of heat stress on dairy traits, measured with an index of temperature and relative humidity (THI). A 'repeatability animal model' and a 'reaction norm animal model' were used to estimate genetic (co)variance components. Estimates obtained with both models were very similar. The h(2) of daily yields in MG did not vary throughout the THI scale, but the pattern of variation of content traits showed negative trends for increasing THI values. In PYA, a slight positive tendency throughout the THI scale was observed for the same traits. The genetic correlations between subsequent points in the THI scale were lower than 0.80 when they were computed between low and high THI points. The same reaction norm was observed for all traits. Using the 'reaction norm animal model', it was possible to identify those animals that show the same performance throughout the THI trajectory (robust) and those with varying performances (tolerant and non-tolerant to heat stress). Results in this study also show that heat tolerance decreases, while the genetic level for milk traits increases. Losses because of heat stress were equivalent to 1.9 and 3.1% in the yearly yield of fat and protein for MG and PYA, respectively.
将穆尔西亚-格拉纳迪纳（MG）和帕约亚（PYA）奶山羊的月度产奶量和成分测试日记录与气象站的天气数据相结合，分析了热应激对奶山羊产奶性状的影响，这些性状通过温度和相对湿度指数（THI）来衡量。采用“重复动物模型”和“反应规范动物模型”来估计遗传（协）方差分量。两种模型得到的估计值非常相似。MG 的日产量 h(2)在整个 THI 范围内没有变化，但含量性状的变化模式显示出随着 THI 值的增加呈负趋势。在 PYA 中，同一性状在整个 THI 范围内表现出轻微的正趋势。在计算低 THI 和高 THI 点之间的遗传相关系数时，THI 范围内的后续点之间的遗传相关系数低于 0.80。所有性状都表现出相同的反应规范。使用“反应规范动物模型”，可以识别出在整个 THI 轨迹中表现相同性能的动物（稳健）和性能不同的动物（对热应激有耐受性和无耐受性）。本研究的结果还表明，耐热性降低，而奶性状的遗传水平增加。MG 和 PYA 的脂肪和蛋白质的年总产量因热应激而损失分别相当于 1.9%和 3.1%。
