Sire Evaluation By Second Lactation Records of Daughters

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Abstract
A model describing the selection of cows to have a 2nd lactation is developed. This model allows for factors independent of milk yield in 1st lactation to influence the variable upon which selection is based. Under this model a procedure for estimating the biases in best linear unbiased predictors, which assume no selection, is presented. This procedure was used to obtain estimates of biases for 1109 Holstein sires in artificial insemination in the northeastern USA. Estimated biases for assumed selection models were small relative to changes in ranking of bulls from 1st to 2nd lactations of daughters. Rank correlation was .77 between rank of bulls based on 1st lactation and rank for 2nd lactations of daughters where selection is ignored.