Dong M C, Van Vleck L D
Department of Animal Science, Cornell University, Ithaca, NY 14853.
J Dairy Sci. 1989 Jul;72(7):1933-6. doi: 10.3168/jds.S0022-0302(89)79313-9.
Estimates of genetic correlations were .17 between first lactation milk yield and concurrent calving interval, .10 between second lactation milk yield and first calving interval, and .82 between first and second milk yields. Corresponding phenotypic correlations were .27, .16, and .58. Heritability estimates were .27 and .25 for first and second lactations and .15 for calving interval. Estimates were averages of two samples of 15 New York State herds averaging 144 AI-sired Holstein cows and 30 sires. Milk yields were 305-d, mature equivalent. Calving interval was days between first and second freshening. First milk records without a second freshening were included. Multiple-trait animal model included separate herd-year-season effects for first and second milk yields and calving interval. Numerator relationships among animals within herd, except for daughter-dam relationships, were included. The REML with the expectation-maximization algorithm was used to estimate (co)variance matrices among genetic values and environmental effects for the three traits. Results indicate a need to adjust milk records for the phenotypic effects of current and previous calving interval. The genetic association, however, between fertility and milk yield appears small. Genetic improvement of 450 kg of milk yield may result in 2 added d to first calving interval.
头胎产奶量与同期产犊间隔的遗传相关性估计值为0.17，二胎产奶量与头胎产犊间隔的遗传相关性估计值为0.10，头胎和二胎产奶量之间的遗传相关性估计值为0.82。相应的表型相关性分别为0.27、0.16和0.58。头胎和二胎产奶量的遗传力估计值分别为0.27和0.25，产犊间隔的遗传力估计值为0.15。这些估计值是对纽约州15个牛群的两个样本的平均值，每个样本平均有144头人工授精的荷斯坦奶牛和30头公牛。产奶量为305天的成熟当量。产犊间隔是第一次和第二次产犊之间的天数。包括没有第二次产犊的第一次产奶记录。多性状动物模型包括头胎和二胎产奶量以及产犊间隔的单独畜群-年份-季节效应。包括畜群内动物之间的分子关系，但不包括女儿-母亲关系。使用带有期望最大化算法的REML来估计三个性状的遗传值和环境效应之间的（协）方差矩阵。结果表明，需要根据当前和先前产犊间隔的表型效应对头胎产奶记录进行调整。然而，繁殖力和产奶量之间的遗传关联似乎很小。产奶量遗传改良450千克可能会使头胎产犊间隔增加2天。
