An updated version of lifetime net merit incorporating additional fertility traits and new economic values
Lifetime net merit (NM$) is an economic selection index intended for use by commercial dairy producers. The current version of NM$ was most recently updated in 2010, and includes information from 13 traits in Holsteins, 11 in Brown Swiss, and 9 in the other dairy breeds. A new version of the index, 2014 NM$, now includes heifer (HCR) and cow (CCR) conception rates to provide more complete information about fertility. Additional benefits of fertility that are not included in productive life (PL) are earlier age at first calving, decreased units of semen needed per pregnancy, decreased labor and supplies for heat detection, synchronization, inseminations, and pregnancy checks, additional calves produced, and higher yields because more optimal lactation lengths are achieved. The total value of HCR including age at first calving, insemination costs, heat detection, pregnancy checks, and reproductive culling was $2.25; CCR was $2.25; and DPR was $11. Replacement heifers were previously assumed to cost $1940, but current prices are only about $1200 to 1500. Lower replacement prices will reduce the value of PL and daughter pregnancy rate (DPR) because fewer lactations are needed to recover costs. Fertility traits will receive a combined emphasis of 8.6%, less than the 11% on DPR in 2010 NM$. Relative emphasis for PL will decrease to 17% from 22% in 2010. DHI mean SCC has decreased from 230,000 in 2002 to 200,000 in 2012. Therefore, the actual change in SCC from a 1-unit change in SCS and actual SCC differences among bull daughters are now much less than when SCC premiums were introduced. The premium / 1,000 cells increased only slightly since 2010 and contributes much of the SCS economic value, but the smaller phenotypic mean and SD for SCC will decrease the relative emphasis to 8% on SCS from 10% in 2010.. Only slight revisions are needed to the milk and components prices forecast in 2010 NM$, but yield traits will receive more relative emphasis if PL, SCS, and fertility get less emphasis. These changes will increase the relative emphasis on yield to 42% from 35% in 2010. The 2014 NM$ index is correlated by 0.966 with 2010 NM$ for recent progeny-tested bulls. An increase in genetic progress worth $8 million/year is expected on a national basis, assuming that all of the changes are improvements and that all breeders select on NM$.
Keywords: economic values, lifetime net merit, selection index