家畜育种值的群体间转换

Conversion of Estimated Breeding Values between Populations

根据 Falconer 提出的关于一个家畜在不同环境的表现可看作是不同的性状的思想,并利用方差组分估计的极大似然法。本文提出了一个估计育种值的群体间转换因子 a 和 b的新方法——MTML 法.并用模拟资料将此方法与前人提出的最小二乘法(OLS)和 Wilmink法进行了比较.结果表明,3种方法都给出了 a 的无偏估值。但由 MTML 法所得到的 a 估值的标准误最小.用 Wilmink 法能得到 b 的无偏估值,但其标准误最大.而用 MTML 法所得到的b估值虽略有下偏,但其标准误最小.在多数情况下,用 MTML 法可得到最小的转换育种值的均方误.OLS 法和 Wilmink 法都极大地受抽样方式的影响。而 MTML 法则几乎不受影响.

A.new method for estimating the factors a and b used for the conversion of estimated breed- ing values from one country to another is presented.This method is based on the Falconer's concept that the performances of an animal in different environments can be considered as different traits and on the estimation of variance-covariance components by the Maximum Likelihood method.A comparison of this method with the ordinary least squares (OLS) method and the method of Wilmink was made using simu- lated data.It was shown that all the three methods gave unbiased estimates of a ,but the estimates from the new method had the smallest standard errors.The method of Wilmink yielded unbiased estimates of b but with the largest standard errors.Whereas the new method yielded downwards estimates of b but with the smallest standard errors.In most cases the new method gave the smallest mean squared errors (MSE) of the converted breeding values,and OLS the largest.The OLS and the Wilmink method were greatly affected by the way of selecting animals for exporting,whereas the new method was hardly affect- ed.