Six health traits will be incorporated into Holstein sire evaluations in April 2018. The traits include hypocalcemia, displaced abomasums, ketosis, mastitis, metritis and retained placentas. More breeds will be added as more information for each bred is accumulated.
The evaluations will be presented as percentage points of each disease resistance event above or below breed average. A higher, positive value equals greater resistance than breed average, while a negative number equates to less resistance than breed average, explains Kristen Gaddis, a geneticist with the Council for Dairy Cattle Breeding (CDCB).
For example, the Holstein breed average incidence of mastitis is 10%. If a sire’s mastitis resistance evaluation is +3, it means his daughters on average will have a mastitis incidence of 7%. Conversely, if a sire’s mastitis resistance is -3, his daughters on average will have a mastitis incidence of 13%.
The health traits will also be incorporated into indexes such as NetMerit$ so dairy farmers can get an estimate of total economic value. The health traits are correlated to other traits already in the indexes, such as productive life and liveability. CDCB and USDA geneticists have taken these correlations into account so that the traits aren’t double counted, says Gaddis.
Only the direct cost of each health trait will be used: Hypocalcemia, $34; DAs, $197; ketosis, $28, mastitis, $75; metritis, $112, and RPs, $68. The heritability of each trait is relatively low: Hypocalcemia, 0.6%; DAs, 1.1%; ketosis, 1.2%, mastitis, 3.1%; metritis, 1.4%, and RPs, 1%. Nevertheless, genetic resistance to the traits is additive and permanent, so over time and over generations, disease resistance can be built up and accumulated.
Preliminary health trait evaluations will be done in December 2017, but released only to Dairy Records Processing Centers, AI organizations (on animals each owns), breed associations and nominators (animals for which they submit genotypes). These preliminary evaluations will be non-official and are being offered to these groups for educational purposes only. They will not be publicly released.