|Van Vleck, Lloyd|
Submitted to: Brazilian Journal of Genetics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/24/1999
Publication Date: N/A
Interpretive Summary: The phenomenon when the maternal effect of a cow is influenced by the maternal effect of her dam can be modeled by having three genetic effects in the model for genetic evaluation for a trait such as weaning weight. The three genetic effects are those due to the genotype of the calf (direct), the calf's dam (maternal) and the dam of the calf's dam (grandmaternal). That influence, if present, often is represented by a fast growing heifer (high milk yield of mother) having reduced maternal ability herself. This pattern has been thought to exist in breeds such as Hereford which typically exhibit a strong negative covariance between direct and maternal genetic effects. When grandmaternal effects have been included in models for those breeds, estimates of variance due to maternal genetic effects have increased, i.e., maternal effects are shown to be even more important when grandmaternal influence is accounted for. Analyses of weights of Gobra acattle of Senegal have shown strong maternal effects through 18 months of growth and high negative genetic correlations between direct and maternal effects. In this study of African cattle, however, no evidence was found for influence of grandmaternal effects in spite of a pattern of direct and maternal inheritance similar to that of Hereford and Angus cattle in the United States. In the United States, genetic evaluations of beef cattle should be adjusted for grandmaternal effects but that adjustment is not needed for Gobra cattle.
Technical Abstract: Estimates of genetic parameters were obtained for birth (n=3909), weaning (n=3425), yearling (n=2764) and final (n=2144) weights from records of Gobra cattle collected at the Centre de Recherches Zootechniques de Dahra (Senegal). Three animal models were fitted to obtain estimates by REML using an average information (AI) method. Model 1 considered random direct, ,maternal genetic and maternal permanent environmental effects. In Model 2, a general grandmaternal effect was added to the random effects considered in Model 1 and in Model 3, the general grandmaternal effect was divided into grandmaternal genetic and grandmaternal permanent environmental effects. All models allowed covariances among genetic effects. Inclusion of grandmaternal effects in the models (Models 2 and 3) did not change the estimates of genetic parameters compared to Model 1. Estimates of variances due to grandmaternal effects tried to become negative and were set to zero except for yearling weight for which grandmaternal heritability was .03 plus/minus .03 and .03 plus/minus .02), weaning (.20 plus/minus .05 and .21 plus/minus .05), yearling (.26 plus/minus .07 and .16 plus/minus .07) and final (.14 plus/minus .06 and .16 plus/minus .06) weights. The esti- mates of the genetic correlation between direct and maternal effects for birth, weaning, yearling and final weights were -.17 plus/minus .40, -.58 plus/minus .32, -.52 plus/minus .34 and -.34 plus/minus .37, respectively. For yearling weight, Model 3 gave estimates of the genetic correlations between direct and grandmaternal effects and between maternal and grand- maternal effects of .28 plus/minus .48 and -.33 plus/minus .67, respectively.