Abstract
A genetic analysis was conducted on preweaning and postweaning growth and carcass composition records from steers produced in two long-term crossbreeding studies. In phase I, Angus (A), Brahman (B), Brangus (BR), Charolais (C) and Hereford (H) sires produced straightbred, F$\sb1$, back-cross, three-breed cross and 2- and 3-breed rotational crossbred steers (N = 708) from 1960 to 1968. Straightbred, F$\sb1$, back-cross, three-breed cross and 2-, 3- and 4-breed rotational crossbred steers (N = 1530) were produced from 1970 to 1988 by A, B, C and H sires in phase II. Direct and maternal additive and non-additive genetic effect contrasts were obtained. Heritabilities and genetic and phenotypic correlations were estimated for phase I using a multivariate mixed sire model and for phase II using an animal model. Direct additive genetic effects of B were smaller than the other direct additive genetic effects for hot carcass weight, total lean yield, marbling score and tenderness but not different than the average non-Brahman additive genetic effect for carcass weight adjusted ribeye area. Maternal additive genetic effects were smaller than direct additive genetic effects for carcass traits. Direct heterosis effects involving B were positive and larger than heterosis effects not involving B. Maternal heterosis effects were near zero for carcass traits. The ranking of genetic effects in phases I and II were similar. Heritability estimates for postweaning growth and carcass traits were moderate to large, except in the case of daily gain on ryegrass, which had a low heritability. Genetic correlations indicated a high association among weights, rates of gain and total lean yield. Increased growth and carcass weight had negative phenotypic and genetic correlations with carcass weight adjusted ribeye area. Genetic correlations among fat and meat quality traits were small, although the association between marbling score and Warner-Bratzler shear force tended to be favorable. Preweaning growth traits had positive correlations with carcass traits related to weight and total lean yield. Increasing percentage B was a significant source of heterogeneity among estimates of genetic and phenotypic (co)variances for ribeye area and Warner-Bratzler shear force.
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