Núñez-Dominguez R, Van Vleck L D, Cundiff L V
Roman L Hruska U.S. Meat Animal Research Center, ARS, USDA, Clay Center, NE 68933, USA.
J Anim Sci. 1995 Oct;73(10):2940-50. doi: 10.2527/1995.73102940x.
The purpose of this study was to evaluate the effect of adjusting for heterogeneous variances across breed groups on prediction of breeding values (PBV) of selected sires and on breed of sire effects. Data on weights at birth (BWT), 200 d (WW), and 365 d (YW) of purebred and crossbred calves from matings of Angus (A), Hereford (H), Polled Hereford, Charolais, Shorthorn, Simmental, Limousin, Maine-Anjou, Chianina, Gelbvieh, Tarentaise, and Salers Bulls to A and H cows were used. Calf performance in H and A dams was treated as a different trait. Models compared included fixed birth year, cow age, and sex classes and crossbreeding effect as a covariate; random direct and maternal genetic and permanent environmental effects were also included, but their variance structure was different. Model I assumed homogeneous variances across breed groups. Model II accounted for heterogeneous variances. Sires were ranked based on PBV from each model, and means of PBV of selected sires were calculated based on Model II. Differences between mean PBV were small for BWT, intermediate for WW, and larger for YW. Differences in PBV of selected sires increased as selection intensity increased, but only for WW and YW. Large differences in mean PBV of selected sires between maternal environments (H vs A) were observed for WW and YW for various sire breeds. Means of PBV of selected sires based on Model II exceeded those based on Model I by 6 to 16 kg of YW for various selection intensities and maternal environments. Estimates of breed of sire effects from Model I or II were similar for BWT and WW, but large differences were found for YW. Results indicate that some additional economic returns may be gained by commercial producers if sires are chosen across breeds based on predicted genetic values computed with models accounting for heterogeneous variances.
本研究的目的是评估对不同品种组间的异质方差进行调整，对所选种公牛育种值预测（PBV）以及种公牛品种效应的影响。使用了安格斯（A）、海福特（H）、无角海福特、夏洛莱、短角牛、西门塔尔、利木赞、缅因安茹、契安尼娜、吉尔维耶牛、塔兰泰拉和萨勒斯公牛与A和H母牛交配所产纯种和杂种犊牛出生时体重（BWT）、200日龄体重（WW）和365日龄体重（YW）的数据。H和A母本中的犊牛性能被视为不同的性状。所比较的模型包括固定的出生年份、母牛年龄、性别类别以及作为协变量的杂交效应；还包括随机的直接遗传、母本遗传和永久环境效应，但其方差结构有所不同。模型I假定不同品种组间方差齐性。模型II考虑了异质方差。根据每个模型的PBV对种公牛进行排名，并基于模型II计算所选种公牛PBV的均值。BWT的平均PBV差异较小，WW的差异中等，YW的差异较大。所选种公牛PBV的差异随着选择强度的增加而增大，但仅针对WW和YW。对于不同的种公牛品种，在WW和YW方面观察到所选种公牛在母本环境（H与A）之间的平均PBV存在较大差异。对于不同的选择强度和母本环境，基于模型II的所选种公牛PBV均值比基于模型I的超出6至16千克的YW。模型I或II对种公牛品种效应的估计在BWT和WW方面相似，但在YW方面发现了较大差异。结果表明，如果商业生产者根据考虑异质方差的模型计算的预测遗传值跨品种选择种公牛，可能会获得一些额外的经济回报。
