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ARS Home » Research » Publications at this Location » Publication #91791


item Van Vleck, Lloyd

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/20/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Including grandmaternal effects in models for genetic analysis of weaning weight seems to be important for breeds of beef cattle with large maternal effects. Grandmaternal effects can be thought of as the effect of the maternal grandmother on the maternal ability of the dam of a calf. If important, grand dams that produce the most milk and wean the heaviest daughters tend to produce grandsons and granddaughters with reduced weanin weights, presumably because greater milk consumption of daughters leads to over fattening. Fat deposits in the udder of young heifers interferes with mammary gland development and reduced milk production. Results show that grandmaternal effects exist in some breeds. Probably more importantly, when grandmaternal effects exist, maternal heritabilities may be underestimated and correlations between direct and maternal effects may be biased downward with models typically used to estimate maternal effects for weaning weight. Because of the relatively large standard errors in the present analyses, larger data sets need to be analyzed in order to better qualify the magnitude of biases in different breeds. Larger data sets are needed to allow calculation of rank correlations between estimated breeding values for direct and maternal weaning weights obtained from different genetic models that include or do not include grandmaternal effects to determine whether different animals would be selected as future parents.

Technical Abstract: Weaning weights from nine parental and three composite breeds were analyzed to estimate variance due to grandmaternal genetic effects and to compare estimate for variance due to maternal genetic effects from models with and without grandmaternal effects. Observations ranged from 794 to 3,465. Animals in pedigree file ranged from 1,244 to 4,326. Two single- trait animal models were used to obtain estimates of covariance components by REML using an average information method. Model 1 included random direct and maternal genetic, permanent environmental maternal, and residual environmental effects as well as fixed sex by year and age of dam effects. Model 2 in addition included random grandmaternal genetic and permanent environmental grandmaternal effects to account for maternal genetic effects of a cow on her daughter's maternal genetic effect. Non-zero estimates of relative variance due to grandmaternal effects could be obtained for seven of the twelve breeds, ranging from .03 to .06. Heritability estimates in these breeds were similar with both models. Existence of variance due to grandmaternal effects did not affect estimates of maternal heritability (m2) and the correlation between direct and maternal genetic effects (ram) for Angus and Gelbvieh. For the other five breeds, estimates increased for both m2 and ram. Estimates of correlation between maternal and grandmaternal genetic effects were large and negative. These results suggest that grandmaternal effects exist in some breeds and that maternal heritability may be underestimated and the correlation between direct and maternal genetic effects may be biased downward if grandmaternal effects are not included in the model for weaning weight.