Definition of Group Effects in Sire Evaluation Models

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Abstract
Group effects are used in [cow] sire evaluation models to account for genetic trend. Definitions of these group effects where sires are related were developed. Definitions were obtained for sire groups from results of a set of modified mixed model equations. Definitions were functions of genetic selection differentials. Definitions were dependent on the matrix of numerator relationships. Simulation of 10,000 replicates of a particular population structure was used to evaluate definitions. Three models with different relationship matrices were fit to the data for each replicate. Group solutions were compared to hypothesized group effects computed from realized genetic selection differentials in each replicate. There was close agreement between group solutions and corresponding hypothesized effects.

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