The Council on Dairy Cattle Breeding (CDCB) will be including six health traits in Jersey sire evaluations for the first time in April.
The traits include: Displaced abomasum, milk fever, ketosis, mastitis, metritis and retained placenta. These are the same traits that were made available for Holsteins in 2008.
These health disorders occur relatively infrequently and their heritability (or genetic control) is low. Mastitis has the highest heritability, at 3.1. That’s followed by metritis, 1.4; ketosis, 1.2; displaced abomasum, 1.1; retained placenta, 1.0 and milk fever, 0.6.
The impact of Predicted Transmitting Ability (PTA) of each trait will be a little tricky to discern at first. The PTAs will be the predicted daughter difference for resistance above or below the Jersey breed average, says Duane Norman, CDCB technical advisor. The larger the positive values, the more favorable the genetic resistance to the disorder.
Take mastitis. The frequency that mastitis is recorded in Jersey health records is 10.4%, making the “health trait resistance rate” 89.6 (100 – 10.4). The PTA range is +3.0 to -3.0. So Jersey bull A with a Mastitis PTA of +3.0 is expected to have mastitis resistance rate of 92.6, or 3.0 better than average. Jersey Bull B with a Mastitis PTA of -3.0 is expected to have a mastitis rate of 86.6, or 3.0 worse than average.
“This can also be indicated inversely by stating in the typical Jersey environment, only about 7.4% of the daughters of Bull A will have a mastitis incident, while about 13.4% of Bull B’s daughters will have a mastitis code,” says Norman. “Difference in extra costs and lost milk income from their two alternatives equates to a hefty difference in herd income.”
Geneticists say incorporating these health traits in your selection program is best done through including them in a weighted selection index, rather than selecting bulls on individual traits.
For more detail on these health traits, click here.