Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 28, 1996
Publication Date: N/A
Interpretive Summary: Estimates of the genetic correlation between direct genetic and maternal genetic effects in beef cattle have ranged from small positive to relative- ly large negative value for weaning weight. The difference in milk pro- duction between heifers and older cows can be as much as 30% in dairy cattle. The genetic potential of a calf for growth, however, would be the same if the dam was a heifer or a mature cow, but the milk potential would be different. Thus, the correlation between direct and maternal genetic effects might be different for different parities. Weaning weight records from nine pure and three compsoite breeds at MARC were analyzed to determine the direct genetic-maternal genetic correlation when the dams were 2, 3, or greater than or equal to 4 yr of age. No evidence was found to support the hypothesis that the direct-maternal genetic covariance is different for different ages of dam. Similar direct-maternal genetic covariances for different ages of dams suggest that weaning weights for different ages of dams need not be considered as separate traits. Correla- tions among direct genetic effects and among maternal genetic effects for weaning weight for different ages of dams also support this conclusion. The need to treat weaning weights for each age of dam as separate traits would greatly increase computing requirements for genetic evaluations. The analyses do suggest that direct-maternal genetic covariance for weaning weight may be negative for some breeds, near zero for some breeds and slightly positive for other breeds.
Technical Abstract: Weaning weights of calves of dams at ages in years of 2, 3, and later were modeled to be separate traits. Fixed effects were year and sex combi- nations for nine pure breeds and year-sex-generation combinations for three composite populations. Random effects in each trait were correlated direct and maternal genetic, maternal permanent environmental, and temporary environmental. Direct and maternal effects were correlated across traits. REML with a derivative-free algorithm was used to estimate the 30 (co) variance components. Number of animals per breed group ranged from 1,244 to 4,326. For the three traits for pure breeds, average proportions of phenotypic variance were .34, .31 and .27 for direct genetic; .16, .15 and .12 for maternal genetic; and .18, .20, and .17 for maternal environmental effects. Average correlations among traits were .84 for direct genetic, .78 for maternal genetic, and .71 for maternal environmental effects. Average of direct-maternal correlations for pure breeds was .05. For the composite breeds, average proportions of variance were .44, .46 and .36 for direct genetic; .06, .06 and .05 for maternal genetic; and .16, .14 and .14 for maternal environmental effects. Average correlations among traits were .93 for direct genetic, .76 for maternal genetic, and .85 for maternal environmental effects. Average direct-maternal genetic correlation was .09 for composites. No evidence was found for greater direct-maternal genetic correlation for earlier than for later ages of dam. Sign and magnitudes of direct-maternal correlations seemed to differ among pure breeds and were reflected in composites from those parent breeds.