Ravagnolo O, Misztal I
Department of Animal and Dairy Science, University of Georgia, Athens 30602, USA.
J Dairy Sci. 2002 Nov;85(11):3092-100. doi: 10.3168/jds.S0022-0302(02)74396-8.
The genetic component in heat tolerance for nonreturn rate in Holsteins was estimated using an animal linear model augmented by a random regression on a temperature-humidity index (THI). Data consisted of 18,059 nonreturn rates at 45,60, and 90 d after insemination and 81,674 first-parity test-day milk yields from 78 herds in Florida. The THI on the day of insemination or test day was added to each record. Only first-insemination records were used. The model for nonreturn rate included the effects of herd-year-season, age, days in milk, milk yield, THI as a covariable, regular additive effect, and random regression on THI for heat-tolerance additive effect. With a single-trait model, heritability estimates for NR45, NR60, and NR90 at THI = 70 for first-lactation cows were 0.006, 0.014, and 0.053, respectively. Genetic correlation between regular NR90 and heat tolerance was -0.95. A bivariate analysis for NR90 and test-day milk production yielded a correlation between regular merit and heat tolerance for NR90 of -0.35, substantially lower than by the univariate model, indicating a bias in the univariate estimates caused by ignored selection. The regular genetic correlation between NR90 and milk yield was -0.41. Genetic correlation between heat tolerance for NR90 and heat tolerance for milk yield was -0.04, indicating the need to separate selection.
利用动物线性模型估计荷斯坦奶牛不返情率的耐热性遗传成分，该模型通过对温度湿度指数（THI）进行随机回归进行扩充。数据包括佛罗里达州78个牛群中授精后45天、60天和90天的18059个不返情率，以及81674头初产奶牛的测定日产奶量。授精日或测定日的THI被添加到每条记录中。仅使用首次授精记录。不返情率模型包括牛群-年份-季节、年龄、产奶天数、产奶量、作为协变量的THI、常规加性效应以及THI的耐热性加性效应随机回归的影响。对于初产奶牛，在THI = 70时，单性状模型对NR45、NR60和NR90的遗传力估计分别为0.006、0.014和0.053。常规NR90与耐热性之间的遗传相关性为-0.95。对NR90和测定日产奶量进行双变量分析，得出NR90的常规性能与耐热性之间的相关性为-0.35，远低于单变量模型，表明单变量估计存在因忽略选择而导致的偏差。NR90与产奶量之间的常规遗传相关性为-0.41。NR90的耐热性与产奶量的耐热性之间的遗传相关性为-0.04，表明需要分开选择。
