Genetic Analysis of Some Growth and Carcass Traits in Beef Cattle

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Abstract
Data were obtained from 47 sire progeny groups containing 265 Hereford and Angus steers slaughtered at approximately 13 mo. of age. The steers were divided into five groups by herd and year of birth. Intra-group paternal half-sib analyses of variance and covariance were used to estimate heritabilities and genetic, environmental and phenotypic correlations. The heritability estimates obtained for carcass weight per day of age, rib-eye area, rib-eye area per 100 lb. carcass, backfat thickness, carcass grade, carcass yield grade, and estimated percent retail cuts were 0.39, 0.73, 0.29, 0.43, 0.62, 0.36 and 0.40, respectively, indicating that selection for any of these traits would be effective. The genetic correlations obtained indicate that genes for rapid growth are not antagonistic to those for the production of desirable carcasses, except that a slight increase in backfat thickness may be expected. The major genetic antagonism evidenced in this study was between carcass grade and percent retail cuts. Environmental and genetic correlations influencing the phenotypic correlation between a particular pair of traits differed substantially in some instances. Thus, the phenotypic correlations frequently were not indicative of the underlying genetic relationship.