|Van Vleck, Lloyd|
Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/9/1997
Publication Date: N/A
Interpretive Summary: Cytoplasmic genetic effects are transmitted directly from mother to off- spring. A father does not transmit cytoplasmic genetic effects. Cyto- plasmic effects have been reported for yield and component traits of dairy cattle. If such effects are significantly different from zero and are not accounted for, progress from selection can be reduced. Records from 138,869 lactations of 68,063 Holstein cows were divided into 10 samples. Each sample averaged 4,926 dams but only 2,026 cytoplasmic lines. Other effects on the model included direct and maternal genetic effects as well as interactions between sires and herds. Averaged over the 10 samples fractions of total variation due to cytoplasmic effects were about 1% to less than 1% for milk and fat yields and fractions of fat in the lactation yield. These estimates suggest that cytoplasmic effects can be ignored in genetic evaluations of dairy sires and cows for yields of milk and fat and fraction of fat with the result that genetic evaluations can be done less expensively than if cytoplasmic effects needed to be in the model used for genetic evaluations.
Technical Abstract: Milk and fat yields and fat percentage (2x, 305-d, ME) in the first three lactations of New York Holsteins were used to estimate variances due to direct and maternal genetic, cytoplasmic sire by herd interaction and cow permanent environmental effects. Cytoplasmic line was traced to last female ancestor using DHI records from 1950 through 1991. Records were 138,869 lactations of 68,063 cows freshening from 1980 through 1991. Ten random samples were based on herd code. Each sample averaged 4,926 dams and 2,026 cytoplasmic lines. Model also included herd-year-seasons as fixed effects and direct-maternal genetic covariance. Average estimates of maternal genetic variances and maternal-direct covariances, as fractions of phenotypic variances, were .008 and .007 for milk; .010 and .010 for fat and .006 and .025 for fat%, respectively. Average fractions of variance due to cytoplasmic line were .011, .008, and .009 for milk and fat tyields and fat %. Dropping maternal genetic effects and maternal-direct covariance from the model increased fraction of direct genetic variance by .014, .021 and .046 for milk, fat and fat %, with little change in fraction due to cytoplasmic line. Excluding cytoplasmic effects from model increas- ed ratio of additive direct genetic to phenotypic variance by less than 2%. Similarly, when sire by herd interaction was excluded, direct genetic to phenotypic variance ratio increased 1% or less.