PARAMETER ESTIMATES FOR DIRECT, MATERNAL, AND GRANDMATERNAL GENETIC-EFFECTS FOR BIRTH-WEIGHT AND WEANING WEIGHT IN HEREFORD CATTLE

Birth and weaning weights adjusted for age of dam from four lines of H ereford cattle were analyzed to determine the relationships among gran dmaternal, maternal, and direct genetic effects. Three lines were sele cted for 1) weaning weight (WWL), 2) yearling weight (YWL), and 3) an index of yearling weight and muscle score (IXL). The fourth line was a n unselected control Line (CTL). Numbers of observations ranged from 1 ,699 (CTL) to 2,811 (WWL), and number of animals in the pedigree file ranged from 2,266 to 3,192. Two animal models were used to obtain esti mates by REML using an average information method. Model 1 included ra ndom direct and maternal genetic, permanent maternal environmental, an d residual environmental effects, and fixed sex x year effects. Model 2 additionally included random grandmaternal genetic and permanent gra ndmaternal environmental effects. For birth weight, Models 1 and 2 gav e almost identical estimates for direct and maternal heritability, and for the fraction of variance that was due to maternal permanent envir onmental effects. Estimates for grandmaternal heritability could be ob tained only for IXL (.03) and CTL (.01). For weaning weight, estimates for direct heritability were similar from both models. Estimates far maternal heritability from Model I were .18,.20,.13, and .20, and corr esponding estimates from Model 2 were .34, .31,.13, and .34 for WWL, Y WL, IXL, and CTL, respectively. For IXL, estimates for variances that were due to grandmaternal genetic and grandmaternal permanent environm ental variances could not be obtained and were set to zero. Grandmater nal heritability estimates for WWL YWL, and CTL were .05, .09, and .12 . Estimates of correlations between direct and maternal genetic effect s were -.13, -.44, -.11, and -.26 for WWL, YWL, ML, and CTL. Estimates of correlations between direct and grandmaternal genetic effects were .21, .83, and .55, and those between maternal and grandmaternal genet ic effects were -.99, -.84, and -.76 for WWL, YWL, and CTL, respective ly. These results indicate that grandmaternal effects may be important for weaning weight and that maternal heritability may be underestimat ed if grandmaternal effects are not included in the model.