The lifetime net merit (NM$) index ranks dairy animals based on their combined genetic merit for economically important traits. Indexes are updated periodically to include new traits and to reflect prices expected in the next few years. The August 2018 update of NM$ includes genetic evaluations for 6 new health traits recorded by producers: clinical mastitis (MAST), ketosis (KETO), retained placenta (REPL), metritis (METR), displaced abomasum (DA), and milk fever (MFEV; hypocalcemia). Cows with genes that keep them healthy are more profitable than cows with health conditions that require extra farm labor, veterinary treatment, and medicine.
Economic values of the 6 new traits were obtained as averages of 2 recent research studies plus additional yield losses not fully accounted for in published genetic evaluations for yield traits. Liang et al. (2017) estimated direct treatment, labor, and discarded milk costs for health disorders from veterinary and producer survey responses, and Donnelly (2017) obtained health treatment costs from 8 cooperating herds in Minnesota. Some yield losses associated with health conditions are not fully accounted for when 305-day lactation records include adjusted test days that are coded as sick or abnormal. Total costs for the 6 traits are added to NM$ in the form of a health trait subindex (HTH$) that is not published separately. This is similar to the calving trait subindex (CA$) that combines 4 traits and is not published or to conformation traits, which are grouped into an udder composite, feet and leg composite, and body weight composite (BWC).
Relative emphasis on most other traits was slightly less because of the addition of HTH$. However, yield trait emphasis increased slightly and somatic cell score (SCS) emphasis decreased greatly because correlated health costs previously assigned indirectly to yield and SCS are now assigned directly to HTH$. Other economic values were updated very little. The 6 health traits are currently evaluated only for Holsteins. The 2018 and 2017 NM$ (VanRaden, 2017) indexes were correlated by 0.994 for recent Holstein bulls.
To read the full report, visit the USDA AIPL website HERE.
