Bar-Anan R, Ron M, Wiggans G R
J Dairy Sci. 1983 Mar;66(3):595-600. doi: 10.3168/jds.S0022-0302(83)81830-X.
Genetic correlations between Predicted Difference for first and second, first and third, and second and third lactations milk were .82, .62, and .94 and for Predicted Difference percent fat .94 for the three associations. Regression coefficients for following on previous lactation Predicted Difference were less than unity; thus, Predicted Difference from first lactation might be overweighted when age adjusted and pooled with second and third lactations. Regressions of Predicted Difference milk of sons on sires for first, second, third, and pooled lactation records were .32 +/- 18, .42 +/- .21, .56 +/- .31, .35 +/- .15, and intraclass correlations between half brothers were .09 +/- .08, .28 +/- .11, .25 +/- .11, and .12 +/- 10. Predicted Differences for second and third lactations were, thus, near the theoretical expectation of .5 and .25 for regressions of son on sire and between half-brother correlations but lower for Predicted Differences of first and pooled lactations. Variance of Predicted Difference of first lactation between sires of sons was small compared with the variance of sons within sires. It was postulated that effective selection on the sire-to-sire path on Predicted Difference of first lactation had reduced predictability on the sire-to-sire improvement path. An interaction of sire by number of lactations may be inferred from the incomplete genetic correlations between Predicted Differences of first and following lactations and from the reduction in the variance between sire in first but not in later lactations. Progeny tests of single lactation seem warranted for the production profile of dairy sires.
头胎与二胎、头胎与三胎、二胎与三胎泌乳量预测差异之间的遗传相关性分别为0.82、0.62和0.94，三种组合的预测脂肪百分比差异的遗传相关性为0.94。前一胎泌乳量预测差异对下一胎的回归系数小于1；因此，在进行年龄调整并将头胎与二胎和三胎泌乳量合并时，头胎泌乳量预测差异可能被高估。头胎、二胎、三胎以及合并泌乳记录的儿子的泌乳量预测差异对父亲的回归系数分别为0.32±0.18、0.42±0.21、0.56±0.31、0.35±0.15，半同胞之间的组内相关系数分别为0.09±0.08、0.28±0.11、0.25±0.11和0.12±0.10。因此，二胎和三胎泌乳量预测差异接近儿子对父亲回归以及半同胞相关系数的理论预期值0.5和0.25，但头胎和合并泌乳量预测差异较低。与同一父亲的儿子之间的方差相比，不同父亲的头胎泌乳量预测差异的方差较小。据推测，对头胎泌乳量预测差异的父系到父系路径进行有效选择，降低了父系到父系改良路径的可预测性。从一胎与后续泌乳量预测差异之间不完整的遗传相关性以及一胎但非后续泌乳期不同父亲之间方差的降低，可以推断出父亲与泌乳次数之间存在相互作用。对于奶牛种公牛的生产概况，似乎有必要进行单胎泌乳的后代测试。
