Modified contemporary comparison sire evaluations from first, all, and later lactations.

Modified Contemporary Comparisons are calculated by the United States Department of Agriculture from first and later lactations, results of which form the published progeny evaluations for all lactations. Characteristics of such evaluations on 200 Holstein sires, each with more than 500 daughters in each data set in the Summer 1981 run, were studied. Predicted Differences for milk averaged 245, 286, and 292 kg for first, all, and later lactation evaluations, with standard deviations of 271, 253, and 254 kg. The average difference (later minus first) was 47 kg (standard deviation, 149 kg). Average absolute difference was 123 kg (standard deviation, 97 kg). Correlations were .95 between first and all, .84 between first and later, and .97 between all and later. The correlation between progeny test for first lactation and difference was -.38 (-.28 for absolute difference). Percent of first lactations culled was correlated -.49, -.47, and -.37 for first, all, and later evaluations. Important variables in prediction of later lactations were first, percent of firsts culled, and sire's age, with first alone producing a coefficient of determination of .71. Sire's age was correlated -.11, -.19, and -.23 with first, all, and later evaluations indicating possible differences in genetic trend for first and later progeny tests for these sires. Fat yield behaved similarly to milk except that correlations between progeny tests and sire's age or culling were less than for milk. Ranking of bulls for daughter milk yield in later lactation changed from first lactation.