Using the Cow Livability Index
Last August, predicted transmitting abilities for cow livability (PTA LIV) were introduced. The trait predicts a cow’s ability to remain alive in the milking herd, explains Kathy Lee, a dairy geneticist with Michigan State University.
The trait records how many daughters of a bull die during lactation. That’s important, because these animals have no salvage or cull cow value, and actually cost the farmer money to dispose of the carcass.
On the other hand, bulls with a higher cow livability PTA allow for selective culling and an income stream from the cows that are culled.
PTA LIV is not yet included in the Net Merit $ index, allowing farmers some time to learn how to use the trait. “The heritability of cow livability is 1.3,” says Lee. “Although the heritability is low, there is value in including PTA LIV in a herd’s selectin program due to the significant economic impact of the trait.”
She uses this example. Assume bull A has a PTA LIV of +2.6 and Bull B has a PTA LIV of -1.1. “In an average herd with 83% of the cows remaining alive during their lifetime, 85.6% of Bull A’s daughters will remain alive. For Bull B, 81.9% of his daughters are expected to leave the herd alive,” she says.
In a herd of 100 cows, the difference is 3.7 cows (85.6-81.9). “If the average value of a cull cow is $1,000, the difference in cull cow income would be $3,700,” she says.
“Based on August 2016 data, the average PTA LIV for Active AI bulls is +0.8%. The range was -6.0 to +6.6%. The top 20% of the Active AI bulls for PTA LIV was at 2.7% or higher,” says Lee.
Note: This story appears in the February 2017 issue of Dairy Herd Management.
