Genetic selection for cow livability
Keeping cows alive in the milking herd impacts dairy herd profitability. Genetic evaluations for cow livability are now being calculated for U.S. dairy cattle.
December 5, 2016 - Author: Kathy Lee, Michigan State University Extension
Two factors that impact dairy herd profitability are cow longevity in the milking herd and how cows leave the herd. Genetic evaluations for productive life (PL) of dairy cows have been available in the United States since 1994. PL is a prediction of how long a cow is expected to remain in the milking herd. Her status at removal is not considered, that is was she culled or did she die.
In August 2016, predicted transmitting abilities for cow livability (PTA LIV) were reported for the first time as an additional genetic selection tool. Cow livability predicts a cow’s ability to remain alive while in the milking herd.
The status of a cow when leaving the herd is important. Cows that are culled have some salvage value, whereas no income is generated by dead cows. In fact, some cost will be incurred to dispose of the cattle mortality.
The average cow mortality rate is 6 percent each lactation. Considering the average cow has 2.8 lactations, the death loss of U.S. dairy cows is approximately 17 percent during their lifetime in the milking herd. That means that 83 percent of the cows remain alive, and dairy producers can make decisions about which of these cows to cull.
Using genetic evaluations for cow livability
The heritability of cow livability is 1.3 percent. Although the heritability is low, there is value in including cow livability in a herd’s genetic selection program due to the significant economic impact of the trait.
Let’s look at a comparison of two bulls. Bull A has a PTA LIV of +2.6 and the PTA LIV for Bull B is -1.1. In an average herd with 83 percent of the cows remaining alive during their lifetime, 85.6 percent of Bull A’s daughters will remain alive. For Bull B, 81.9 percent of his daughters are expected to leave the herd alive.
If there are 100 daughters of each bull in a herd, the difference for the two bulls in the number of daughters remaining alive would be 3.7 (85.6 minus 81.9). If the average value of a cull cow is $1,000, the difference in cull cow income would be $3,700.
Based on August 2016 data, the average PTA LIV for Active AI bulls was +0.8 percent. The range was -6.0 to +6.6 percent. The top 20 percent of the Active AI bulls for PTA LIV were at +2.7 percent or higher.
Using selection indexes is an effective way to incorporate several economic important traits into sire selection decisions. Future plans are to include PTA LIV in Net Merit (NM$) and the other lifetime merit indexes. Michigan State University Extension published the article It’s time to update sire selection goals which describes NM$.
For the August and December 2016 genetic evaluations, the Council of Dairy Cattle Breeding (CDCB) has chosen not to incorporate PTA LIV into any of the lifetime merit indexes. This allows dairy producers to become familiar with cow livability as a stand-alone trait before it becomes part of various selection indexes.
Take time to look at the PTA LIV data for your herd’s service sires when the next genetic evaluations are released in early December. Based on its economic importance, cow livability warrants inclusion in a herd’s genetic program.