VARIANCES OF DIRECT GENETIC-EFFECTS, MATERNAL GENETIC-EFFECTS, AND CYTOPLASMIC INHERITANCE EFFECTS FOR MILK-YIELD, FAT YIELD, AND FAT PERCENTAGE

Milk yield, fat yield, and fat percentage during the first three lacta tions were studied using New York Holsteins that were milked twice dai ly over a 305-d, mature equivalent lactation. Those data were used to estimate variances from direct and maternal genetic effects, cytoplasm ic 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 o f 68,063 cows calving from 1980 through 1991. Ten random samples were based on herd code. Samples averaged 4926 dams and 2026 cytoplasmic li nes. Model also included herd-year-seasons as fixed effects and geneti c covariance for direct-maternal effects. Mean estimates of the effect s of maternal genetic variances and direct-maternal covariances, as fr actions 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 wer e 0.011, 0.008, and 0.009 for milk yield, fat yield, and fat percentag e. Removal of maternal genetic effects and covariance for maternal dir ect effects from the model increased the fraction of direct genetic va riance by 0.014, 0.021, and 0.046 for milk yield, fat yield, and fat p ercentage; 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 o f direct genetic variance to phenotypic variance increased 1% or less.