Suárez M J, Munilla S, Cantet R J C
Advanta Semillas SAIC-Nutrisun Business Unit, Balcarce Biotechnology Center, Balcarce, Argentina.
J Anim Breed Genet. 2015 Feb;132(1):21-9. doi: 10.1111/jbg.12121. Epub 2014 Oct 15.
Animals born by embryo transfer (ET) are usually not included in the genetic evaluation of beef cattle for preweaning growth if the recipient dam is unknown. This is primarily to avoid potential bias in the estimation of the unknown age of dam. We present a method that allows including records of calves with unknown age of dam. Assumptions are as follows: (i) foster cows belong to the same breed being evaluated, (ii) there is no correlation between the breeding value (BV) of the calf and the maternal BV of the recipient cow, and (iii) cows of all ages are used as recipients. We examine the issue of bias for the fixed level of unknown age of dam (AOD) and propose an estimator of the effect based on classical measurement error theory (MEM) and a Bayesian approach. Using stochastic simulation under random mating or selection, the MEM estimating equations were compared with BLUP in two situations as follows: (i) full information (FI); (ii) missing AOD information on some dams. Predictions of breeding value (PBV) from the FI situation had the smallest empirical average bias followed by PBV obtained without taking measurement error into account. In turn, MEM displayed the highest bias, although the differences were small. On the other hand, MEM showed the smallest MSEP, for either random mating or selection, followed by FI, whereas ignoring measurement error produced the largest MSEP. As a consequence from the smallest MSEP with a relatively small bias, empirical accuracies of PBV were larger for MEM than those for full information, which in turn showed larger accuracies than the situation ignoring measurement error. It is concluded that MEM equations are a useful alternative for analysing weaning weight data when recipient cows are unknown, as it mitigates the effects of bias in AOD by decreasing MSEP.
如果受体母牛的信息未知，通过胚胎移植（ET）出生的动物通常不纳入肉牛断奶前生长的遗传评估。这主要是为了避免在估计未知的母牛年龄时产生潜在偏差。我们提出了一种方法，允许纳入母牛年龄未知的犊牛记录。假设如下：（i）代孕母牛属于正在评估的同一品种；（ii）犊牛的育种值（BV）与受体母牛的母体BV之间没有相关性；（iii）所有年龄的母牛都用作受体。我们研究了固定水平的未知母牛年龄（AOD）的偏差问题，并基于经典测量误差理论（MEM）和贝叶斯方法提出了一种效应估计器。在随机交配或选择的情况下使用随机模拟，在以下两种情况下将MEM估计方程与BLUP进行了比较：（i）完整信息（FI）；（ii）一些母牛缺少AOD信息。来自FI情况的育种值预测（PBV）的经验平均偏差最小，其次是未考虑测量误差时获得的PBV。反过来，MEM显示出最高的偏差，尽管差异很小。另一方面，对于随机交配或选择，MEM的MSEP最小，其次是FI，而忽略测量误差产生的MSEP最大。由于MSEP最小且偏差相对较小，MEM的PBV经验准确性高于完整信息，而完整信息又比忽略测量误差的情况显示出更高的准确性。得出的结论是，当受体母牛未知时，MEM方程是分析断奶体重数据的一种有用替代方法，因为它通过降低MSEP减轻了AOD偏差的影响。
