Trends in Genetic Merit of Dairy Sires at Initial Proving

Abstract

Initial Modified Contemporary Comparison sire summaries from 1974 through 1978 were studied for 16,791 dairy sires of six breeds. These sires were grouped into five classes. Sires sampled through artificial insemination units were in one group; natural service sires further classified by number of herds (1, 2 to 3, 4 to 6, and 7+) in the initial (first published) proof were in the other four groups. Initial Repeatabilities of the progeny test for sires in these five classes were about 40, 18, 23, 29, and 35%.Genetic merit (pedigree indexes and Predicted Differences) was increasing over the 5 yr. Regressions of either measure of merit on year sampled averaged 19kg of milk and .6kg of fat. Bulls sampled through artificial insemination organizations were superior to natural service bulls in pedigree index and initial Predicted Difference. Genetic merit of widely sampled natural service sires showed no consistent advantage over natural service sires sampled in single herds.The initial sire summaries were compared with the most recent summary through 1978. There was a slight tendency for later summaries to average higher for all classes of sires. Sires sampled by artificial insemination organizations were more likely to increase in Predicted Difference.