Definition of Group Effects in Sire Evaluation Models

Abstract

Group effects are used in sire evaluation models to account for genetic trend. The objective of this paper was to develop definitions of these group effects where sires are related. 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. © 1983, American Dairy Science Association. All rights reserved.