U.S. Genetic Base Change: April 2025

The U.S. genetic base will be updated with the CDCB evaluations on April 1, 2025. The CDCB merit index values, along with the 49 individual selection traits and composites produced by CDCB, will be expressed on an updated genetic base relative to dairy cows born in 2020. In the U.S., this update occurs every five years to best align selection tools with the current dairy herd.

UPDATE REGARDING CALVING TRAITS
The genetic base change occurring with the April 2025 evaluations will not be applied to calving traits – Daughter Calving Ease, Sire Calving Ease, Daughter Stillbirth and Sire Stillbirth. Calving traits are an independent trait group in which the genetic evaluations are reported on an observed (phenotypic) scale. This means that both genetic and phenotypic bases need to be updated during a base change. When these base updates were applied for the April evaluation, unanticipated results were observed. Due to the timing of this discovery, CDCB decided to maintain calving traits in their current base in April. This means that both genetic and phenotypic bases used to calculate these traits in December 2024 will again be applied during this run. New phenotypes received in the National Cooperator Database since the December evaluation will be included. CDCB expects to update the bases for calving traits in August after further investigation can be conducted. Maintaining the calving traits’ bases in the April evaluation will not impact any other traits. More information will be shared as it becomes available.

Preliminary estimations of the changes in Predicted Transmitting Ability (PTA) values for all breeds are available at https://uscdcb.com/basechange. The final base change values, genetic versus environmental impact, and additional resources will be shared in late March.

2025 Genetic Base Change