The August U.S. dairy genetic evaluations, released Aug. 7, now include disease resistance that is incorporated into four Net Merit Indexes.
Genetic evaluations for six health traits—displaced abomsum, hypocalcemia, ketosis, mastitis, metritis and retained placenta—were introduced by the Council on Dairy Cattle Breeding (CDCB) in the April evaluations. Combined into a sub-index, these six traits are now known at HTH$.
With the August evaluations, those traits were assigned economic values and incorporated into Net Merit (NM$), Cheese Merit (CM$), Fluid Merit (FM$) and Grazing Merit (GM$). In NM$, health traits make up 2.3% of the index. In CM$, they make up 1.9%; in FM$, 2.3% and in GM$, 2.1%. For even more detail, click here.
“Dairy producers can select for any combination of traits, but total genetic progress will be fastest using an index,” says Dr. Paul VanRaden, Research Geneticist at USDA’s Animal Genomics and Improvement Laboratory. “Because many traits affect profitability, total profit usually increases when more traits are included in the selection index if the evaluations are accurate and correct economic values are used.”
Relative emphasis on most other traits reduced slightly due to the addition of HTH$; however, yield trait emphasis increased slightly and somatic cell score (SCS) emphasis decreased greatly because of correlated health costs now assigned directly to HTH$, he says.
“The actual benefits from adding health traits may not appear as large as some expect – because other traits such as productive life, SCS, fertility, livability and calving ease also directly or indirectly account for impacts on animal health,” says VanRaden.
He adds that a handful of other changes were implemented by CDCB for the August evaluations and can be viewed at the CDCB website.