The genetic base for U.S. genetic evaluations changed this month. Every five years the base is changed to adjust the predicted transmitting abilities (PTAs) for dairy animals (bulls, cows, heifers and calves) for the genetic progress that has occurred during the past five years, explains Kathy Lee, Michigan State University extension dairy educator. In January, the base or reference population changed to cows born in 2005.
The average PTAs within each breed for cows born in 2005 will be zero, except for somatic cell score, calving ease, and stillbirth rate which are centered at breed average.
Genetic base changes do not change the relative ranking of animals or the genetic merit of the animals. Only the reference point for calculating PTAs changes.
Source: Michigan State University