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Mixed Model Methodology for Unifying Within-Herd and National Beef Sire Evaluation¹

Iowa State University, Ames 50011

Abstract

A mixed model has been developed for the unification of beef cattle within-herd evaluations and national beef sire evaluation. The model accounts for both sire and dam effects and is used to obtain predictors of individual animal genetic merit for traits of economic importance. The prime purpose of the unification is to provide a link between herds for determining best linear unbiased predictors (BLUP) of expected progeny differences (EPD) for yearling bulls and heifers that are comparable across herds. The method of unification builds within-herd mixed model evaluation equations for herd dams, contemporary groups and sires on a herd-by-herd basis. Dams and contemporary group equations are absorbed into sire equations for each herd. After absorption, the sire equations are consolidated from all herds to form a set of national sire evaluation equations. Single-trait BLUP are determined for the sires and are used in back-solving for within-herd contemporary group estimates and dam predictors. Young animal EPD for traits of interest are computed as a function of their parent EPD plus their own regressed performance. Sire growth EPD for the 1984 American Hereford and American Angus sire evaluations were determined using this new methodology to develop sire equations consolidated across herds.

¹ Journal Paper No. J-11744 of the Iowa Agr. and Home Econ. Exp. Sta., Ames. Project No. 2000. This research was funded in part by a grant from the American Angus Assoc., St. Joseph, MO.