Albuquerque L G, Keown J F, Van Vleck L D
Department of Animal Science, University of Nebraska, Lincoln 65883-0908, USA.
J Dairy Sci. 1998 Feb;81(2):544-9. doi: 10.3168/jds.S0022-0302(98)75606-1.
Milk yield, fat yield, and fat percentage during the first three lactations were studied using New York Holsteins that were milked twice daily over a 305-d, mature equivalent lactation. Those data were used to estimate variances from direct and maternal genetic effects, cytoplasmic effects, sire by herd interaction, and cow permanent environmental effects. Cytoplasmic line was traced to the last female ancestor using DHI records from 1950 through 1991. Records were 138,869 lactations of 68,063 cows calving from 1980 through 1991. Ten random samples were based on herd code. Samples averaged 4926 dams and 2026 cytoplasmic lines. Model also included herd-year-seasons as fixed effects and genetic covariance for direct-maternal effects. Mean estimates of the effects of maternal genetic variances and direct-maternal covariances, as fractions of phenotypic variances, were 0.008 and 0.007 for milk yield, 0.010 and 0.010 for fat yield, and 0.006 and 0.025 for fat percentage, respectively. Average fractions of variance from cytoplasmic line were 0.011, 0.008, and 0.009 for milk yield, fat yield, and fat percentage. Removal of maternal genetic effects and covariance for maternal direct effects from the model increased the fraction of direct genetic variance by 0.014, 0.021, and 0.046 for milk yield, fat yield, and fat percentage; little change in the fraction was due to cytoplasmic line. Exclusion of cytoplasmic effects from the model increased the ratio of additive direct genetic variance to phenotypic variance by less than 2%. Similarly, when sire by herd interaction was excluded, the ratio of direct genetic variance to phenotypic variance increased 1% or less.
利用纽约荷斯坦奶牛研究了头三个泌乳期的产奶量、产脂量和乳脂率。这些奶牛每天挤奶两次，进行为期305天的成熟当量泌乳期。利用这些数据估计直接遗传效应、母体遗传效应、细胞质效应、公牛与牛群互作效应以及奶牛永久环境效应的方差。通过1950年至1991年的奶牛性能测定记录（DHI）追溯细胞质系至最后一个雌性祖先。记录包括1980年至1991年68063头产犊奶牛的138869个泌乳期。基于牛群编码选取了10个随机样本。样本平均有4926头母畜和2026个细胞质系。模型还包括牛群 - 年份 - 季节作为固定效应以及直接 - 母体效应的遗传协方差。母体遗传方差和直接 - 母体协方差效应的平均估计值（作为表型方差的一部分），产奶量分别为0.008和0.007，产脂量分别为0.010和0.010，乳脂率分别为0.006和0.025。细胞质系方差的平均比例，产奶量、产脂量和乳脂率分别为0.011、0.008和0.009。从模型中去除母体遗传效应和母体直接效应的协方差后，产奶量、产脂量和乳脂率的直接遗传方差比例分别增加了0.014、0.021和0.046；细胞质系导致的比例变化很小。从模型中排除细胞质效应后，加性直接遗传方差与表型方差的比率增加不到2%。同样，当排除公牛与牛群互作效应时，直接遗传方差与表型方差的比率增加1%或更少。
