|Van Vleck, Lloyd|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/19/1999
Publication Date: N/A
Interpretive Summary: Weaning weight of a beef calf is influenced by its genes for growth plus the genes of its mother for mothering ability (milk primarily). Both traits (direct growth and maternal ability) are economically important for selection. Knowledge of the genetic correlation between genes for growth and for maternal ability is important because the first information on a sire is the growth (direct) of his calves. From that first information, th breeding value for direct growth is predicted. At the same time, the breeding value for maternal ability is predicted based on the genetic correlation between direct and maternal genetic effects and the predicted breeding value for direct growth. Often the correlation is estimated to be negative but various explanations exist as to why the true correlation may be nearly zero or positive. This study of Angus field data compared the effects of 1)a covariate for dam's own weaning weight, 2) grandmaternal effects, and 3) sire by herd by year interactions in the model as ways to explain the observed direct maternal correlations. Grandmaternal effects and sire by herd-year interaction were more important than a covariate for dam's own WWT. The results suggest that sire by herd-year interaction effects should be included in models for national genetic evaluation (NCE) of beef cattle for weaning weight. Grandmaternal effects, although less important, should also be included in NCE if computationally feasible.
Technical Abstract: Weaning weights from nine sets of Angus field data were analyzed. Six animal models were used to compare two approaches to account for an environmental dam-offspring covariance and to investigate effects of sire herd-year (SH) interaction on estimates of genetic parameters. Model 1 included random direct and maternal genetic, maternal permanent environmental, and residual effects. Fixed effects were age of dam, age at weaning and herd-year-management-sex combination. Possible influence of dam's phenotype on daughter's maternal ability was modeled by including a covariate for maternal phenotype (Model 3) or by fitting grandmaternal genetic and permanent environmental effects (Model 5). Models 2, 4, and 6 were based on Models 1, 3, and 5, and additionally included SH interaction effects. With Model 3, estimates of the regression coefficient and the (co)variances were obtained by REML. Estimates of the regression coefficient ranged from -.003 to .014, and (co)variance estimates were similar to those from Model 1. With Model 5, grandmaternal heritability estimates ranged from .02 to .07, and estimates of maternal heritability and direct-maternal correlation increased compared to Model 1. With models including SH, estimates of fraction of phenotypic variance due to SH interaction effects were from .02 to .10. Estimates of direct and maternal heritability were smaller and estimates of the correlation were greater than with models without SH interaction effects. Interaction effects of SH were more important than the covariate or grandmaternal effects. The direct maternal correlation may be biased downward if SH interaction or grandmaternal effects are not included in models for weaning weight.