Changes of evaluation for natural-service sampled bulls brought into artificial insemination.

United States Department of Agriculture Sire Summary files were used to select bulls with a published Modified Contemporary Comparison sire evaluation prior to entry into artificial insemination. Canadian bulls were not included. Of the Brown Swiss, Guernsey, Holstein, and Jersey bulls that entered artificial insemination since 1974, 28 Brown Swiss, 19 Guernseys, 298 Holsteins, and 45 Jerseys (4 to 12%) had natural service evaluations. Of these bulls, 10 Guernseys, 154 Holsteins, and 28 Jerseys had an increase of Repeatability of 30% or more after entering artificial insemination. Evaluations for bulls just prior to their entering artificial insemination were compared with their most recent evaluations through July 1983. Average Repeatabilities for evaluations of bulls just prior to their entering artificial insemination were 32% for Guernseys, 32% for Holsteins, and 31% for Jerseys and 88, 90, and 87% for their most recent evaluations. Average Predicted Differences prior to entering artificial insemination were 305 kg for Guernseys, 394 kg for Holsteins, and 452 kg for Jerseys for milk and 11, 10, and 16 kg for fat. Most recent average Predicted Differences were 268, 380, and 532 kg for milk and 7, 10, and 18 kg for fat. Predicted Differences of natural service bulls were not overevaluated regardless of number of herds for sampling or year of entry into artificial insemination. Artificial insemination organizations can continue to acquire bulls with natural service evaluations calculated with the Modified Contemporary Comparison and be confident that these Predicted Differences are not overestimated.