Observed and Theoretical Genetic Trends in a Large Dairy Population Under Intensive Selection

Abstract

Animal model estimated breeding values for milk, fat, and protein yields were studied for Italian Friesian cows born from 1972 to 1988. Annual genetic progress for these traits increased from .08 genetic SD/yr prior to 1984 to .25 to .30 genetic SD/yr from 1985 to 1988. The latter trends—double previously reported estimates—were related to selection intensities and generation intervals of sires and dams of bulls and replacements. Selection intensities of sires of bulls and replacement females were very high, because proven sires annually were from 200 Italian and 1500 North American bulls. Italian Friesian bull-dams were in the top 1% of 150,000 cows. Their 3.7-yr generation interval also accelerated genetic progress. Progress of .36 genetic SD/yr calculated from component pathways exceeded that observed from 1985 to 1988, and was only slightly lower than theoretical progress of .38 genetic SD or 3.4% of mean yield. These rates of annual genetic progress are achievable with stringent selection of bull-sires among the 3000 now proven annually in Europe and North America and with use of the top 1% of the cow population. As the gap between different populations narrows, progeny test schemes must be more efficiently managed to ensure current rates of genetic progress.