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Revision of Ancestor Merit for Modified Contemporary Comparison Sire Evaluations

Animal Improvement Programs Laboratory, Agricultural Research Service, United States Department of Agriculture, Beltsville, MD 20705

ABSTRACT

Procedures for computing ancestor merit for Modified Contemporary Comparison sire evaluations were extended for protein and modified to improve accuracy and account for genetic trend for bulls without evaluated ancestors. Sire Summaries of bulls evaluated in October 1974 or later were analyzed to determine difference between daughter Modified Contemporary Deviation and pedigree index. Bulls were identified by birth year, sampling program, and pedigree information available. Means of differences weighted by Repeatability were computed for breed, parity group, yield trait, and pedigree category. Means were smoothed by linear regression over 9 consecutive yr centered on year for which mean was being estimated. Means for recent years were calculated from regression coefficients from last complete set of 9 yr. Ancestor merit, which when weighted by 1 minus Repeatability is pedigree contribution to Predicted Difference, was calculated as appropriate difference plus bull's pedigree index. Changes made in calculation of ancestor merit accounted for genetic trend in bulls without pedigree information available. Ancestor merit procedures were made self-updating to eliminate the assumption that trend estimated in the past will continue unchanged.