The release of the April 2025 Council on Dairy Cattle Breeding (CDCB) proof will come with several important changes. First the April 2025 proof will include a base change affecting all traits evaluated by CDCB. Secondly, the NM$ and TPI formulas will be adjusted to account for new economic values within the formulas. It is critical to understand these changes, so that you can make informed selection and breeding decisions based on CDCB evaluations.
WHAT IS A CDCB BASE CHANGE?
When an animal’s genomic sample is sent to an evaluation laboratory such as Genetic Visions-ST™, the DNA of that animal is compared to a reference population or a group of animals with production, management, and/or classification data in CDCB’s National Cooperator Database. This allows the CDCB to make predictions about the predicted transmitting ability (PTA) of that animal or how that animal will contribute to many different production, health, reproductive and type traits. This reference population has been updated every 5 years since 1980 and is known as the genetic “base”. When the base is updated, as it will be in April 2025, the reference population is updated to reflect the genetics of the current population of animals. The current base population includes animals born in 2015 and in April 2025, the base will be updated to include animals born in 2020. For most traits, the average PTA is set to 0 with the exception of Somatic Cell Score, Calving Ease, and Stillbirth Rate, and all animal’s PTAs are adjusted based on the new average. In Figure 1, you can see an example of 3 different cows born in 2015, 2020, and 2022. In the Un-Adjusted [2020] base, the animal born in 2015 represents the average of 0, while in the Base Adjusted [April 2025] column, the animal born in 2020 represents the average of 0.
BASE CHANGE
Cows born in 2020, reset their transmitting ability to zero and adjust all other animals acordingly
Exception: somatic cell score, calving ease, and stillbirth rate, which are centered at breed average rather than zero.
It is important to note that the genetic merit of the animals in Figure 1 did not change, however their PTAs were adjusted to reflect the comparison of their genetics to the current population of animals.
HOW WILL PTAS BE ADJUSTED AFTER THE APRIL 2025 PROOF?
All males and females of all dairy breeds evaluated at CDCB prior to April 2025 and after proof will receive an adjustment to their PTAs to reflect their current genetic value compared to the new base. For a quick reference of the adjustments for Holsteins, please reference Figure 2.
WHAT CHANGES ARE BEING MADE TO THE NM$ FORMULA IN APRIL 2025?
The Lifetime Net Merit (NM$) formula calculated by the CDCB is a comprehensive index that includes the most relevant economic traits to rank animals based on their lifetime profitability. The current formula includes 12 individual traits and 5 composite subindexes. Changes to the NM$ formula occur regardless of the base change to account for changes in economic variables. In the April 2025 revision, no new traits will be added to the NM$ formula, however, the emphasis on the current traits will be changed to reflect new estimates for trait values and account for income and cost variables. Figure 3 and Figure 4 compare the relative emphasis on each trait in the 2021 and 2025 NM$ formulas.
WHAT CHANGES ARE BEING MADE TO THE TPI FORMULA IN APRIL 2025?
Similar to the NM$ formula, the Total Performance Index (TPI) formula includes economically relevant traits in a weighted index to assist producers in ranking animals based on total profitability. The TPI formula includes a 46% emphasis on production traits, 28% emphasis on Health and Fertility Traits, and 26% Emphasis on Conformation traits. Figure 5 shows the TPI formula which is essentially a weighted PTA multiplied by a multiplier with the addition of a constant value which is described in Figure 6. The multiplier is applied to adjust the standard deviations (variance) of the index to keep TPI values unaffected by the base change, so TPI values can be compared across time. The constant is added to put back the reduction in the mean due to the CDCB base change. The constant value of 2363 will be changed to 2845 after the April 2025 proof to account for genetic improvement over the last five years. This process will not affect animal rankings.
Within the TPI formula there will also be a slight change to the Feed Efficiency formula. Figure 7 shows the current formula for Feed Efficiency and the April 2025 revision.
April Proof 2025 will be an exciting proof with multiple changes including a genetic base change, and NM$ and TPI formula revisions. To view all of the latest proof data for STgenetics® bulls and females tested at Genetic Visions-ST™, go to stgen.com or log in to your STrategy™ profile. STgenetics® is proud of the genetic advancements that have been made in the past 5 years in the dairy industry that are reflected in the new base change. We will continue to produce the most profitable and sustainable genetics and partner with our customers to continue to make progress for future generations.
STgenetics®: The best way to predict the future is to create it.
To view full information in PDF format, please click blue button "Open File" below.