Accuracy of First Lactation Versus All Lactation Sire Evaluations by Best Linear Unbiased Prediction

Variances of errors of prediction for sire evaluations which included only first records and for those with records of all lactations were compared for bulls of Ayrshire, Guernsey, Jersey, and Brown Swiss breeds used by artificial insemination with daughters having Dairy Herd Improvement records processed at the New York Dairy Records Processing Laboratory. The model for best linear unbiased prediction included fixed effects of sire group and herd-year-season of freshening and random effects of sires within group, sire-by-herd interaction (to account for environmental correlation among paternal sisters), cow within sire and herd, and residual. Variances of solutions for group effects were generally small relative to variances of prediction errors for sire effects. Using all lactation records, however, reduced variances of group solutions by 7 to 14% for groups of sires used artificially and by 20 to 24% for groups used in natural service. Use of all lactation records decreased the variance of prediction error of the sire solutions so that 15 daughters per sire with all lactations gave accuracy equivalent to 25 daughters using only first records; use of all lactation records with 25 daughters gave accuracy equivalent to 40 daughters with only first records. Genetic progress per year from selection of bulls to sire daughters would be expected to be 10 to 15% greater with use of all lactation records than with use of only first lactation records. The comparable increase from selection of bulls to sire replacement bulls would be 3 to 10%. These theoretical increases must be weighed against possible biases from use of records other than first lactation