|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 7/1/1999
Publication Date: N/A
Technical Abstract: Estimates of genetic correlation between direct and maternal effects for early weights of beef cattle often are negative. Studies of field records have shown that including sire by year interaction and grandmaternal effects improve the model and change the estimate of the direct-maternal genetic covariance. This analysis involved 9,968 progeny records from a long-term selection program (1960-1985) in Herefords. Traits were birth (BW) and weaning (WW) weights, pre-weaning gain (WG), post-weaning gain (YG), and muscle score (MS). The most complete models included fixed effects of sex-line, sex-year, and age of dam-line and random direct, maternal, and grandmaternal genetic, maternal and grandmaternal permanent environmental and either sire by year-sex or sire by year interaction effects. For BW, grandmaternal and sire interaction effects were not important. For WG and WW, including grandmaternal effects was important and dincreased maternal heritability with no change in direct-maternal (d-m) correlation. Sire by year interaction had little effect on estimates of genetic parameters. For YG, grandmaternal model reduced magnitude of negative d-m correlation although maternal heritability was only .03. Further addition of sire interaction effects resulted in slightly positive d-m correlation. The best model included grandmaternal and sire by year by sex interaction effects. For MS, a maternal effects model was significantly better than a direct effects model. Sire by sex-year accounted for .01 of variance and did not affect other parameter estimates. Grandmaternal and sire interaction effects were not important. These data did not show any effect of sire by year interaction on estimates of direct-maternal genetic correlation or maternal heritability for weaning weight.