Ferris T A, Schneider J C, Mao I L
Department of Animal Science, Michigan State University, East Lansing 48824-1225.
J Dairy Sci. 1990 May;73(5):1327-36. doi: 10.3168/jds.S0022-0302(90)78799-1.
After accounting for year of birth of bulls, younger dams produced superior sons. Bulls' PD, parent average, and pedigree index milk decreased with increasing age of dams at bull's birth. This appears to be due to decrease in maternal grandsire's PD milk and dam's Cow Index milk with increase in age of dam. Younger dams have an advantage of potentially higher genetic merit due to genetic trend but have less information included in their evaluations. Bull's latest parent average and pedigree index overestimated latest PD milk. This overestimation was not different with age of dam at bull's birth, suggesting that the bias in predicting bulls' PD from eventual evaluations of dams chosen at a younger age is not different than for dams chosen at a later age. Data were for 2826 bulls sampled by four AI organizations and born between 1965 and 1981. The increase in PD milk of bulls was about 27 kg/yr, but the trend was larger (45 kg/yr) during the last 5 yr. Inclusion of dam's age did not improve prediction of bull's PD milk. Maternal grandsire's PD milk was the primary variable associated with dam's age that accounted for lower bull's PD milk, mainly because older dams tended to have sires of lower genetic merit.
在考虑公牛出生年份后，较年轻的母牛所生的公牛更优秀。公牛的生产性能（PD）、亲本平均值和系谱指数产奶量随着公牛出生时母牛年龄的增加而降低。这似乎是由于随着母牛年龄的增加，外祖父的PD产奶量和母牛的奶牛指数产奶量下降所致。较年轻的母牛由于遗传趋势具有潜在更高遗传价值的优势，但在评估中包含的信息较少。公牛最新的亲本平均值和系谱指数高估了最新的PD产奶量。这种高估与公牛出生时母牛的年龄无关，这表明从较年轻年龄选择的母牛的最终评估中预测公牛PD的偏差与较晚年龄选择的母牛没有差异。数据来自四个人工授精组织抽样的2826头公牛，出生于1965年至1981年之间。公牛的PD产奶量每年增加约27千克，但在过去5年中趋势更大（每年45千克）。纳入母牛年龄并未改善对公牛PD产奶量的预测。外祖父的PD产奶量是与母牛年龄相关的主要变量，这导致公牛的PD产奶量较低，主要是因为年龄较大的母牛往往拥有遗传价值较低的公牛。
