Genetic Variation in Total and Differential Growth of Carcass Components in Beef Cattle

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Abstract
Data were obtained on 503 steers in 75 sire progeny groups from a heterosis experiment involving Angus, Hereford and Shorthorn cattle. They were slaughtered at an average age of about 452 days and the right side of each carcass was processed into essentially boneless trimmed retail cuts with no more than .75 cm. of fat on any surface. Three analyses were made. In one, traits were regressed on age to evaluate variation in growth of retail product, fat trim and bone. Carcass weight was the covariate in the second analysis to evaluate variation in proportion retail product, fat and bone. The third analysis included age and weight as covariates to evaluate differential growth. The effects of year, breed of sire, breed of dam and their interactions were taken into account in least squares analyses used. Paternal half-sib estimates of heritability, genetic and phenotypic variance and genetic, environmental and phenotypic correlation were derived. The results indicate that heritability and phenotypic variance is greater for growth of retail product than for proportion or differential growth of retail product. Estimates of genetic correlation indicate that selection to change proportion of retail product from various wholesale cuts to total retail product would not be effective. Selection for growth of retail product would lead to increased retail product, fat trim, bone and carcass weight without altering over-all carcass composition if slaughter age were held constant. Selection for growth of retail product would gradually increase percent retail product and reduce percent fat trim if carcass weight was standardized by slaughtering at increasingly younger ages. Selection for retail product adjusted for carcass weight would gradually result in increased percent retail product and bone and reduced percent fat due to high positive genetic correlation between retail product and bone and high negative genetic correlation between retail product and fat trim. It appears that selection for weight of retail product from the round adjusted for carcass weight would be essentially as effective in increasing proportion of retail product from the carcass as selection for weight of retail product from the entire carcass adjusted for carcass weight. The heritability and phenotypic variance for retail product to bone ratio were quite low due to high genetic correlations between retail product and bone. Copyright © 1969. American Society of Animal Science . Copyright 1969 by American Society of Animal Science

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