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Virginia Cooperative Extension - Knowledge for the CommonWealth

Genetic base to change in February 2005

Dairy Pipeline: December 2004 and January 2005

Bennet Cassell
Extension Dairy Scientist,
Genetics and Management
(540) 231-4762 email:

National genetic evaluations will use a new base beginning in February 2005, and average proofs for most traits will decline as a result. The genetic base is the zero point against which all cows and bulls are compared for each trait. For the past five years, the genetic base has been set by cows born in 1995. Under the previous base, the average cow born in 1995 had a PTA of zero for most traits evaluated by USDA - production, productive life, other fitness traits. The breed societies used similar genetic bases for evaluations of type traits. In February 2005, the genetic base will be set by cows born in 2000. These cows have inherited all the genetic progress that has taken place in the five-year period between the two genetic bases. The table below summarizes the average change in PTA's for Holstein and Jersey cows. If a bull's PTA for each of these traits was unchanged from Nov 04 to Feb 05, his PTA in Feb 05 would be his Nov 04 PTA minus the values shown in the table. Keep in mind that proofs also change because of new information added between the summaries.

Table 1. Average change in PTA's for different traits for Holstein and Jersey cows born in 2000 compared to cows born in 1995.
Trait Holstein cows Jersey cows
Net Merit ($) 155 128
Milk (lbs) 592 442
Protein (lbs) 19 16
Productive life (mo) 0.3 0.4
SCS (scores) 0.01 0.01
Udder composite (sd units) 0.36 0.25
Feet/legs composite (sd units) 0.31 0.15
Daughter pregnancy rate (%) -0.1 -0.1
Daughter calving ease (%) -0.4  

The figures show how rapidly cows are changing for the various traits, but the information is historic. Mating decisions that produced the cows born in 1995 were made at least ten years ago, while the decisions that produced cows in the new genetic base are already five years old or more. The figures may not represent current rates of genetic change. Some facts are clear, however. Genetic progress for production and type traits was strong and genetic progress for fitness traits other than productive life were small but undesirable. We did make some nice gains in productive life in the period represented in the table. It is my view that dairy producers should pay more attention to SCS, fertility, and calving ease traits and less to type and production in the years ahead. That doesn't mean that progress for type and production needs to cease, but the kinds of cows that make the good milk records certainly does need to change. We need cows that are able to sustain body reserves through the months of high production to improve the odds that they remain fertile, healthy, and relatively trouble-free. That's a different standard of type (specifically dairy form) than we have emphasized in the past.

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