Submitted to: Beef Improvement Federation Proceedings
Publication Type: Proceedings
Publication Acceptance Date: July 6, 2005
Publication Date: July 6, 2005
Citation: Van Raden, P.M. 2005. An example from the dairy industry: the net merit index. In: Proceedings of the Beef Improvement Federation's 37th Annual Research Symposium and Annual Meeting, July 6-9, 2005, Billings, Montana, pp 96-100. Interpretive Summary: Dairy cattle breeders have improved the profit of their herds by genetic selection for production, conformation, longevity, mastitis resistance, fertility, and calving ease. Today, dairy breeders can choose from the best bulls in the world ranked on their combined economic value for these traits by using the Net Merit index. Net Merit combines economically important traits and places different emphasis on those traits that allows for convenient comparisons among animals. A total of 27 traits are currently measured and evaluated for U.S. dairy animals. These evaluations represent the genetic merit an animal is predicted to transmit to its future offspring (predicted transmitting ability) rather than the animal’s own genetic merit (breeding value); predicted transmitting ability is equivalent to the expected progeny difference reported for beef cattle. Dairy cattle selection is a global industry with annual semen sales of nearly $1 billion from the best few thousand bulls worldwide. Breeders can quickly select the best bulls for overall economic return by using Net Merit. By selecting genetically superior animals, dairy producers increase profitability. Beef cattle breeders would benefit from a similar selection index.
Technical Abstract: Since 1994, USDA has published and updated a selection index called Net Merit that combines economically important traits such as production, conformation, longevity, mastitis resistance, fertility, and calving ease. Net Merit is computed for 18 million U.S. cows and 110,000 bulls from 25 countries. Selection of animals to be parents of the next generation of U.S. dairy cattle is more accurate if all traits of economic value are included in the index. Currently the relative emphases on these traits in the U.S. are: Protein 33%, Fat 22%, Longevity 11%, Udder Health 9%, Fertility 7%, Udder Conformation 7%, Mobility 4%, Size –3%, and Calving Ease 4%. Other countries have similar indexes, but place different emphasis on traits they find economically important. Traits with lower heritability now receive much more emphasis and are included in selection because some have coefficients of variation (standard deviation divided by trait average) larger than those for traditional traits. If an animal has no data for a particular trait, its parent average is substituted. If parent evaluations are missing, unknown parent group solutions or breed averages are substituted. If a particular country has no data for a particular trait, its population average is assumed to equal the U.S. average. Indexes require an estimate for each trait, and even estimates with zero reliability are released so that breeders do not have to guess what estimate was used in the selection index. Breeders can quickly select the best bulls for overall economic return by using Net Merit.