VanRaden P M, Wiggans G R, Ernst C A
Animal Improvement Programs Laboratory, USDA, Beltsville, MD 20705-2350.
J Dairy Sci. 1991 Dec;74(12):4344-9. doi: 10.3168/jds.S0022-0302(91)78630-X.
Information on partial lactations often is included in genetic evaluations by predicting the cow's eventual 305-d yield. Such projected yields have less phenotypic and genetic variation than completed yields but were modeled as having greater or equal variation in evaluations. Analysis of first lactations from 48,424 daughters of 844 Holstein sires indicated that yields predicted early (46 to 75 d) in lactation had less than one-half as much additive genetic variance as completed yields. Multiple-trait REML estimates of genetic correlations of predicted and completed yields were all above .92, indicating that early lactation information is valuable if modeled appropriately. Expanded records with genetic variances equal to those of completed yields and new lactation length weights were derived. Expanded records have larger error variances than either projected or completed yields and, thus, are given less weight when included in animal model evaluations. Genetic gains are expected to increase only .2 to .3%, but more stable genetic evaluations should result from use of expanded records, particularly for animals evaluated primarily from first lactation records in progress.
通过预测奶牛最终的305天产奶量，部分泌乳信息通常会被纳入遗传评估中。这些预测产量的表型和遗传变异比完整产量要小，但在评估中被建模为具有更大或相等的变异。对844头荷斯坦公牛的48424头女儿的头胎泌乳分析表明，泌乳早期（46至75天）预测的产量的加性遗传方差不到完整产量的一半。预测产量与完整产量的遗传相关性的多性状REML估计均高于0.92，这表明如果建模得当，泌乳早期信息是有价值的。由此得出了遗传方差与完整产量相等且具有新的泌乳期长度权重的扩展记录。扩展记录的误差方差比预测产量或完整产量都要大，因此，在纳入动物模型评估时权重较低。预计遗传进展仅会增加0.2%至0.3%，但使用扩展记录应会带来更稳定的遗传评估，特别是对于主要根据正在进行的头胎泌乳记录进行评估的动物。
