Submitted to: Hoard's Dairyman
Publication Type: Popular Publication
Publication Acceptance Date: July 18, 2006
Publication Date: August 25, 2006
Citation: Seykora, T., Van Raden, P.M., Cole, J.B. 2006. Net merit receives face-lift. Hoard's Dairyman. 151(14):557.
The USDA net merit (NM$) economic index was updated for the third time since it was first introduced in 1994. The NM$ index is defined as the difference in expected lifetime profit as compared with the average genetic merit of cows within that breed born in 2000. The August 2006 revision updates economic values and correlations between traits, accounts for a revised definition of productive life (longevity), and includes two new genetic traits: service-sire stillbirth and daughter stillbirth as part of a calving-ability composite that also includes service-sire and daughter calving ease. In the calculation of calving ability, calving ease receives 40% of the emphasis and stillbirth receives 60%. Emphasis on yield traits has decreased over time as additional fitness traits were introduced. Fat and protein yields now account for 46% of NM$. Productive life accounts for 17%. Together somatic cell score (mastitis resistance) and udder composite account for 15%. Reproduction (daughter pregnancy rate and calving ability) accounts for 15%. Body size and feet-and-legs composites account for 4 and 3%, respectively. The correlation between 2003 and 2006 NM$ is 0.975; revising NM$ caused only small changes for most artificial-insemination bulls. However, bulls that are excellent for productive life, daughter pregnancy rate, and calving ability may have gone up considerably in the rankings. The range of evaluations for productive life increased by about 40% because of credit is now given for longer lactations and additional life after 84 months of age. Economic weights for nonproduction traits are the same for all USDA merit indexes regardless of whether they are designed for milk-fat-protein, fluid milk, or cheese markets. When selecting bulls based on NM$, dairy producers should avoid putting minimum standards on individual traits and avoid selecting for economically unimportant traits.