Evaluation of cytoplasmic genetic effects in Miles City Line 1 Hereford cattle.

Mixed-model techniques were used to evaluate the importance of cytoplasmic genetic effects on growth traits in beef cattle. The data used were 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 Hereford cattle (Miles City Line 1). Selection criterion was adjusted yearling weight. Cytoplasmic genetic effects were evaluated as both potential 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 removed 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 for BWT and PREADG. Fixed effects included year of birth, age of dam, sex of calf, and regressions on inbreeding of calf, inbreeding of dam, and age off postweaning gain test (POSTADG only). When cytoplasm was fit as a fixed effect, F-tests for cytoplasmic effects were not significant (P = .10 to .99) for any trait. Inclusion of cytoplasmic source (fixed) in the statistical model reduced residual standard deviations less than .1%. Variance components for cytoplasmic genetic effects were estimated simultaneously with variance components for direct, maternal, direct-maternal covariance, and maternal permanent environment using REML techniques. Cytoplasmic source accounted for .40, .00 and .00% of the phenotypic variance for BWT, PREADG, and POSTADG, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)