GENETIC BASE CHANGE FOR FEBRUARY 2005

Authors: Vanraden, Paul; Tooker, Melvin

Submitted to: AIPL Research Reports
Publication Type: Government Publication
Publication Acceptance Date: 10/25/2004
Publication Date: 11/1/2004
Citation: Van Raden, P.M., Tooker, M.E. 2004. Genetic base change for February 2005. AIPL Research Report Base1 (10-04). Available: http://aipl.arsusda.gov/reference/base2005.htm

Interpretive Summary: Genetic evaluations of dairy cattle are expressed relative to a base population. Changing the base every 5 years allows estimates of genetic merit from new evaluations to be easily compared with those from previous evaluations. Base changes also provide an opportunity to review genetic progress and are a logical time to revise trait definitions and evaluation procedures. In February 2005, the genetic base for USDA-DHIA genetic evaluations will become the average value for cows born in the year 2000. Several improvements to genetic evaluation models will be introduced with the February 2005 base change. The new base changes will make identifying and comparing genetically superior animals easier. By selecting genetically superior animals, dairy producers will increase profitability.

Technical Abstract: The genetic base for dairy cattle evaluations is the average genetic merit of cows born in a given year. Base changes provide an opportunity to review genetic progress and are a logical time to revise trait definitions and evaluation procedures. Changing the base every 5 years allows predicted transmitting abilities (PTA's) from new evaluations to be easily compared with previous evaluations because accumulated genetic gain is subtracted so that all animals are compared with a more recent cow population. In February 2005, the genetic base for USDA-DHIA genetic evaluations will become the average value for cows born in the year 2000. Several improvements to genetic evaluation models will be introduced with the February 2005 base change. Those include adjustments for inbreeding depression and differing standard deviations across lactations, expression of yield PTA's to a 36-month age base instead of a mature equivalent, and a heritability of .12 instead of .10 for somatic cell score. Interbull requires that each country pass strict genetic trend validation tests for each trait in each breed at least every other year. The United States passed the validation tests with the new base changes. Those changes make identifying and comparing genetically superior animals easier. By selecting genetically superior animals, dairy producers will increase profitability.