Rodríguez-Almeida F A, Van Vleck L D, Cundiff L V
Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA.
J Anim Sci. 1995 Sep;73(9):2589-99. doi: 10.2527/1995.7392589x.
The effects of accounting for different phenotypic variances according to sire breed and sex subclasses on estimation of sire breed effects and prediction of expected progeny differences of sires mated to Hereford and Angus cows were investigated. Data consisted of 6,977 and 6,530 records of 200-d (weaning) and 365-d (yearling) weights, respectively, of F1 calves sired by bulls (662 and 661, respectively) of 23 breeds that have been evaluated in the Germ Plasm Evaluation Program at the U.S. Meat Animal Research Center, Clay Center, NE. Models compared included fixed effects of genetic group of sire (samples of sires evaluated at different times), dam breed, sex, birth year of calf and age of dam, plus sire within genetic group and dam within dam breed as random effects. Variance structures were different: Model I assumed homogeneous variances across sire breed-sex subclasses; Model II accounted for differences in phenotypic variance by sire breed and sex subclasses. Differences between estimates of sire group effects obtained with the two models were not significant for either trait. Product-moment and rank correlations between expected progeny differences obtained with Model I and Model II were greater than .93 when computed within each group and .99 or larger when computed across breeds. There were slight changes in the numbers of sires contributed by different breeds to the proportions selected across breeds under different selection intensities when sires were ranked with the two models. However, differences between means predicted under Model II were small when sires were ranked and selected based on the two models. Changes in standard errors of prediction for expected progeny differences and standard errors for estimates of breed effects obtained when adjusting for differences of phenotypic variances, compared to not adjusting, were proportional to the ratios of the phenotypic standard deviations of the sire breeds to the common phenotypic standard deviation.
研究了根据父本品种和性别亚类考虑不同表型方差对父本品种效应估计以及与赫里福德牛和安格斯牛配种的公牛预期后代差异预测的影响。数据分别由美国内布拉斯加州克莱中心肉类动物研究中心种质评估项目中评估的23个品种的公牛（分别为662头和661头）所产F1犊牛的200日龄（断奶）体重记录6977条和365日龄（周岁）体重记录6530条组成。所比较的模型包括父本遗传组（不同时间评估的父本样本）、母本品种、性别、犊牛出生年份和母本年龄的固定效应，以及遗传组内父本和母本品种内母本的随机效应。方差结构不同：模型I假设父本品种 - 性别亚类间方差齐性；模型II考虑了父本品种和性别亚类间表型方差的差异。对于这两个性状，用这两个模型获得的父本组效应估计值之间的差异均不显著。当在每个组内计算时，模型I和模型II获得的预期后代差异之间的积差相关和等级相关大于0.93，当跨品种计算时大于0.99或更大。当用这两个模型对公牛进行排名时，不同品种对不同选择强度下跨品种选择比例所贡献的公牛数量有轻微变化。然而，当根据这两个模型对公牛进行排名和选择时，模型II预测的均值差异很小。与不调整相比，在调整表型方差差异时，预期后代差异预测标准误差和品种效应估计标准误差的变化与父本品种表型标准差与共同表型标准差的比率成比例。
