Prediction of transmitting ability of heifers from genetic evaluations of dams when dams and herdmates are required to have a first record.

Estimated transmitting ability for milk production calculated from only first lactation records was regressed on milk proofs of the sire and maternal grandsire and either estimated transmitting ability of the dam calculated from only first lactations or estimated transmitting ability of the dam calculated from all lactations of a data set in which all cows were required to have milk records of first lactation. Records of 222,576 Holstein heifers in the northeastern United States were analyzed. Partial regression coefficients were similar to those from reports in which all records in the data file were used to estimate transmitting abilities. The partial regression coefficient for estimated transmitting ability of the dam from all lactation records (.17) was smaller than the approximate theoretical regression coefficient (.70). The partial regression coefficient for estimated transmitting ability of the dam calculated from first records (.72) was similar to the approximate theoretical regression coefficient (.80).