Book Description

The objective of this study was to estimate genetic parameters for growth, maturity and carcass traits, and to analyze relationship of each of these traits with mature weight. Growth data utilized in the study consisted of repeated weight measurements of 3044 Angus cows. A Brody growth curve was fitted to the data for each cow individually in order to predict asymptotic (mature) weight, age when animal reached 65% of mature weight, and weights, growth rates, degrees of maturity and relative growth rates at 365 and 550 days of age. Carcass data consisted of 3477 records of steers, including hot carcass weight, back fat-thickness, rib-eye area, cutability and marbling score. Genetic parameters of mature weight were estimated from a single-trait animal model for asymptotic weight, a two-trait animal model for asymptotic and weaning weight, and a two-trait animal model for repeated mature weights (measured after 4 y of age) and weaning weight. Heritability estimates for growth and carcass traits were obtained by restricted maximum likelihood from a set of two-trait animal models considering a given trait and weaning weight which was in the model to account for any effect of culling. Similarly, genetic correlations between mature weight and other traits were obtained from a set of three-trait models. A sample of 29943 animals was used for weaning weight measurements. Fixed effects in the models included weaning, cow and carcass contemporary groups. For the carcass traits the effect of slaughter age was included in the model as a covariate. Random effects in the model included direct genetic, maternal genetic and permanent environmental effects for weaning weight, but only direct genetic and repeated measurements (if in the model) for each of the other traits. Estimates of heritability for mature weight were. 44,.51 and. 57 for the single-trait model with asymptotic weight, two-trait model with asymptotic weight and two-trait model with repeated weights, respectively. The reduced heritability estimate from the single-trait model was most likely due to the effect of culling, thus, a genetic evaluation for mature size should be considered in a multiple-trait model including mature weight as well as some earlier measured growth trait. (Abstract shortened by UMI.).