Photo from Andrea Haines

2025 Genetic Base Change

The routine five-year genetic base change will take place in April 2025.

Preparing for a Genetic Base Change

A genetic base is when the average PTAs (Predicted Transmitting Abilities) of cows born in a specific year are set to zero. In other words, the starting line from which we measure PTAs is moved because of genetic progress.

In April 2025, the genetic base population will move from cows born in 2015 to cows born in 2020. Routine base adjustments, which happen every five years in the United States, allow new evaluations to be easily compared with previous evaluations.

Those involved in setting selection thresholds for mating programs should pay close attention to the anticipated changes. A bull or cow who previously reached standards may not do so in April due to the base change.

How is it calculated?

Average PTA (cows born in 2020)
– Average PTA (cows born in 2015)
Base Change

Changes greater than 0 mean the younger cows have a higher genetic merit than the older cows. April 2025 PTAs will show the inverse effect (i.e. a positive milk value in the chart below will appear as a decrease in milk PTA in April).

Why is it updated every 5 years?

The genetic bases to which (most) dairy traits are expressed in the United States have been updated every five years since 1980. This adjustment schedule allows PTAs to reflect genetic improvement over time while still maintaining stability in evaluations.

Estimated 2025 Genetic Base Change Values

To prepare for the genetic base change in April 2025, CDCB has calculated rounded, estimations of the anticipated changes. These numbers are reported as the change in base populations (2015 vs 2020). Because gains were made across five years for most traits, most of these PTAs will be lowered by the amount shown.

A note of caution, these will not be the exact changes coming because all values will be recalculated before the April 2025 run using more complete and current data. Final values will be shared here in mid-March.

TraitAyrshireBrown SwissGuernseyHolsteinJerseyMilking Shorthorn
Milk1503507575040010
Fat51004520-5
Protein515530150
Somatic Cell Score000-0.100
Productive Life0112.51.50.5
Cow Livability-10.500.50.50
Heifer Livability0.50.2
Daughter Pregnancy Rate-1-0.6-0.5-0.2-0.4-0.5
Heifer Conception Rate-.050.1-0.511.5-0.5
Cow Conception Rate-1-0.5-10.50-0.5
Early First Calving-0.50.50.222-1.5
Gestation Length************
Sire Calving Ease0.1-1
Daughter Calving Ease0-0.5
Sire Stillbirth-2
Daughter Stillbirth-1
Milk Fever/Hypocalcemia**0.10.1
Displaced Abomasum**0.30.2
Ketosis**1-0.1
Mastitis-0.20.75-1
Metritis**10
Retained Placenta0.10-0.1
Residual Feed Intake-40
Final Score0.20.20.20.6*0.60.2
Stature0.60.3-0.10.3*0.60.2
Strength00.10.10*0.20
Dairy Form0.20-0.10.4*0.50.2
Body Depth0.1000*00.1
Rear Legs – Side View-0.10-0.20*0-0.1
Rear Legs – Rear View0.10.10.2*00.1
Rump Angle00.2-0.40*-0.40
Rump Width0.20.10.20.3*0.30.2
Fore Udder Attachment0.50.40.60.9*0.90.2
Rear Udder Height0.40.30.41*0.50.2
Rear Udder Width0.20.20.21*0.10.1
Udder Depth0.50.30.50.7*0.70.2
Udder Cleft0.30.10.10.3*0.20.1
Teat Length-0.1-0.4-0.10.3*0.1-0.1
Front Teat Attachment0.30.20.20.4*0.20.1
Front Teat Placement0.20.30.10.4*0.50.2
Rear Teat Placement0.4*
Teat Placement – Rear View0.10.3
Teat Placement – Side View-0.1
Milking Speed00
Mobility0.10.1

– Trait not calculated and published for breed
* Number calculated and provided by Holstein Association USA
** Value not yet available

What is happening with Net Merit$?

Preliminary calculations of the Lifetime Merit Indexes – Net Merit $, Cheese Merit $, Fluid Merit $, and Grazing Merit $ – indicate favorable genetic gains for all lifetime indexes. However, in April 2025, these indexes will also undergo an adjustment to the economic weights used in the formulas.

Where is additional technical information available?

For those in the industry who require additional technical information such as:
– Performance Differences Attributed to Genetic and Environmental Change
– Comparison of change to previous base change
– Standard deviations

Looking for more information about genetic bases or this change? Try one of these industry resources: