Genetic evaluations for new health traits

New genetic evaluations for six health traits in Holsteins were introduced in April. Incorporating these traits in sire selection decisions can lead to healthier and more profitable future replacement heifers.

In April of this year, the Council on Dairy Cattle Breeding (CDCB) released genetic evaluations for six new health traits for Holstein dairy cattle. The new health traits are ketosis, mastitis, metritis, displaced abomasum, milk fever, and retained placenta. The data used to calculate these new predicted transmitting abilities (PTAs) are collected nationally through the Dairy Herd Improvement Association (DHIA). Strict editing of the health records ensures that reliable data are utilized in the genetic evaluations.

These new PTAs are expressed as a cow’s resistance to the given illness. For example, if a bull has a +3.0 PTA for ketosis, his daughters have the ability to be three percentage points more resistant to ketosis than daughters of a bull with +0.0 PTA for ketosis. Reliabilities of these traits range from 40-50 percent. 

The heritabilities of these traits are: ketosis, 1.2 percent; mastitis, 3.1 percent; metritis, 1.4 percent; displaced abomasum, 1.1 percent; milk fever, 0.6 percent; and retained placenta, 1.0 percent. Although the heritabilities of these traits are low, genetic improvement is additive and permanent. That means even with low heritabilities, farmers can select for these health traits and over time improve resistance to these illnesses in their herds. These traits are positively correlated with productive life and livability, indicating their association with disease resistance.

What does genetic selection for health traits mean for dairy farmers? It could mean hundreds of dollars saved on reduced treatments and lost production. One case of displaced abomasum could cost almost $200. Similarly, an incidence of metritis can cost $112, mastitis $75, retained placenta $68, milk fever $34, and ketosis $28.  Sire selection for these new health traits will increase resistance to these diseases in the resulting offspring. This will lower the occurrence of these illnesses over time thus reducing the costs associated with treatment. This will significantly decrease economic losses for dairy farmers in the future.

Beginning with the August 2018 genetic evaluations, the new health traits of displaced abomasum, ketosis, mastitis, metritis, retained placenta, and milk fever will be incorporated into the Net Merit $ (NM$) index. The traits will have a combined relative emphasis of 2.3 percent in NM$. This will make choosing sires and dams that will produce healthy, profitable replacement heifers an easier task. 

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