Abstract
Field records of purebred Angus bull and heifer calves and Hereford bull calves were analyzed to estimate heritabilities of and correlations among five growth characters; birth, weaning and final test weights and preweaning and postweaning average daily gains (ADG). Hereford heifer calves were included in a separate analysis of weaning weight by itself with a greater number of records. Heritability estimates in all of the analyses where both sexes within the breed were included were consistendy higher for bulls than for heifers. The Angus estimates for sexes pooled, bulls and heifers, respectively, were .40, .49 and .36 for birth weight; .38, .42 and .22 for preweaning ADG; .35, .37 and .21 for weaning weight; .30, .47 and .44 for postweaning ADG; and .36, .43 and .24 for final test weight. The Hereford bull estimates for the same respective characters were .54, .41, .43, .26 and .65. The analysis of Hereford weaning weight for both sexes yielded heritability estimates of .31 for sexes pooled, .36 for bull calves and .30 for heifers. Genetic and phenotypic correlations among characters within each breed and sex and with sexes pooled were estimated. Within-sex genetic correlation estimates were moderate to high (.37 to .97) with the following exceptions: Hereford bulls, birth weight-preweaning ADG = .17; Angus bulls, preweaning ADG-postweaning ADG = .19 and weaning weight-postweaning ADG = .18; and Angus heifers, birth weight-postweaning ADG = .00, preweaning ADG-postweaning ADG = -.11, and weaning weight-postweaning ADG = -.18. The phenotypic correlations were, in general, smaller than the genetic correlations The results supported estimates of genetic parameters from experiment station data and indicated that progress can be expected when selecting for one or more of these characters and that correlated responses in the other characters should be anticipated.
Published Version
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