EVALUATION OF CYTOPLASMIC GENETIC-EFFECTS IN MILES CITY LINE-1 HEREFORD CATTLE

Mixed-model techniques were used to evaluate the importance of cytopla smic genetic effects on growth traits in beef cattle. The data used we re records on birth weight (BWT, n = 4,716), preweaning average daily gain (PREADG, n = 4,428), and postweaning average daily gain (POSTADG, n = 3,476) collected from 1935 through 1989 in a closed line of Heref ord cattle (Miles City Line 1). Selection criterion was adjusted yearl ing weight. Cytoplasmic genetic effects were evaluated as both potenti al fixed and random genetic effects. Cytoplasmic sources (n = 26) were determined based on the foundation female in the maternal lineage of each animal. All foundation females were at least five generations rem oved from any descendant that produced a performance record. An animal model was used to account for all nuclear additive genetic variation among animals. Direct additive effects were estimated for all traits. Maternal additive and permanent environmental effects were estimated f or BWT and PREADG. Fixed effects included year of birth, age of dam, s ex of calf, and regressions on inbreeding of calf, inbreeding of dam, and age off postweaning gain test (POSTADG only). When cytoplasm was f it as a fixed effect, F-tests for cytoplasmic effects were not signifi cant (P = .10 to .99) for any trait. Inclusion of cytoplasmic source ( fixed) in the statistical model reduced residual standard deviations l ess than .1%. Variance components for cytoplasmic genetic effects were estimated simultaneously with variance components for direct, materna l, direct-maternal covariance, and maternal permanent environment usin g REML techniques. Cytoplasmic source accounted for .40, .00, and .00% of the phenotypic variance for BWT, PREADG, and POSTADG, respectively . These results suggest that cytoplasmic genetic effects are not impor tant sources of variation for growth traits in beef cattle.