Differences in modified contemporary comparison sire evaluations from first and later lactations by breed

Sire evaluations from three sets of daughter records, first records only (first), later records after firsts (later), and all records (all) by Modified Contemporary Comparison procedures were used to examine differences in first and later lactation evaluations by breed. January 1984 evaluations for milk for 767 Ayrshires, 3,175 Guernsey, 29,498 Holstein, 3,530 Jersey, and 984 Brown Swiss bulls with 10 or more daughters in each set were used. Average differences between evaluations (later minus first) were 36, 0, 6, 35, and 35 kg milk for Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss bulls. Standard deviations of the difference were 114, 94, 142, 91, and 134 kg, showing considerable sire-to-sire variation in difference. Correlations between evaluations based on first and later records were .84 to .86 for all breeds except .92 for Jerseys. Percent of first lactations culled was correlated .20, .18, .16, .16, and .19 with difference for Ayrshire, Guernsey, Holstein, Jersey, and Brown Swiss, indicating that culling produced larger differences between evaluations for first and later lactations in favor of later evaluations. Prediction of sire evaluation from later records was enhanced by knowledge of sire's age in addition to first evaluation for Guernsey, Holstein and Jersey sires. In these breeds, for a constant first evaluation, and percent culled in first lactation, younger bulls had higher evaluations from later records. This study showed important differences between evaluations from first and later records for all breeds.