As readers take a look at this April’s bull list, they will notice significant differences due to the base change.
“Every five years, we update our genetic base in the United States,"? stated Chad Dechow, associate professor of dairy cattle genetics at Penn State University. “For a five-year period beginning in April of 2020, predicted transmitting ability (PTA) will be expressed relative to an average cow born in 2015,"? said Dechow. “In other words, our ‘genetic base’ will be the average cow born in 2015."?
Overall, genomics has substantially enhanced the rate of genetic progress in Holsteins and Jerseys. That means “numbers"? for traits were lowered in many instances.
A few things we noticed
Not only was there a base change this April, the Council on Dairy Cattle Breeding also made a change to the standard deviation (SD) for the production traits and somatic cell score.
This typically happens once every 10 years. Again, the base change happens once every five years. Both happened this April.
In some breeds, particularly in the Holsteins, the very elite Net Merit (NM$) and Total Performance Index (TPI) bulls appeared to go up ever further when compared to the base because of the increase in standard deviation.
“An increase in the standard deviation spreads out the PTAs. Meaning that the top animals go up and bottom animals go down. This allows the top production animals to gain back a large part of the base change roll back.
When viewing the top group, which is where most people look, those animals made a big gain in their overall indices for TPI."? said Tom Lawlor, executive director of research and development at Holstein Association USA.
Sire calving ease recalibrated
The new Sire Calving Ease (SCE) numbers may take some time to sink in for Holsteins. Since there has been significant improvement in cows calving in easier, those evaluations were updated, too.
As a result the “eyeball test"? on the data suggests that SCE numbers went up on bulls. To a dairyman or dairywoman, that may be counterintuitive as there has been less stress in maternity pens in recent years due to improved calving ease bulls.
April 2020 Hoard's Dairyman Bull List
Top 50 Genomic Holstein Net Merit $, Cheese Merit $, and TPI
Top 50 Daughter Proven Holstein Net Merit $, Cheese Merit $, and TPI
Top 25 Holstein Genomic and Daughter Proven Udders, Feet and Legs, and DPR
Top 25 Holstein SCE and Jersey CM$ and JPI
Top Colored Breeds