DIRECT AND MATERNAL GENETIC COVARIANCES BY AGE OF DAM FOR WEANING WEIGHT

Weaning weights of calves of dams at ages in years of 2, 3, and older were modeled to be three separate traits. Fixed effects were sex of ca lf-year of birth combinations for nine pure breeds and sex of calf-yea r of birth-generation for three composite populations. Random effects fitted for each trait were correlated direct and maternal genetic, mat ernal permanent environmental, and temporary environmental. Direct and maternal effects were correlated across traits. A multiple-trait, der ivative-free REML algorithm was used to estimate the 30 (co)variance c omponents. Number of animals per breed group ranged from 1,244 to 4,32 6. For the three traits for pure breeds, average proportions of phenot ypic variance were .34, .31, and .27 for direct genetic; .16, .15, and .12 for maternal genetic; and .18, .20, and .17 for maternal environm ental effects. Average correlations among the three traits were .84 fo r direct genetic, .78 for maternal genetic, and .71 for maternal envir onmental effects. Average of direct-maternal genetic correlations for pure breeds was .05. For the composite breeds, average proportions of phenotypic variances were .44, .46, and .36 for direct genetic; .06, . 06, and .05 for maternal genetic; and .16, .14, and .14 for maternal e nvironmental effects. Average correlations among the three traits were .93 for direct genetic, .76 for maternal genetic, and .85 for materna l environmental effects. Average direct-maternal genetic correlation w as .09 for composites. No evidence was found for greater direct-matern al genetic correlation for earlier than for later ages of dam. Sign an d magnitudes of direct-maternal genetic correlations seemed to differ among pure breeds and were reflected in composites from those parent b reeds.