The August 2026 genetic evaluations from the Council on Dairy Cattle Breeding (CDCB) introduce the first national genetic evaluations for calf health while also revising long-standing reproductive performance evaluations to better reflect modern dairy management. The release adds Resistance to Diarrhea (DIA) and Resistance to Respiratory Problems (RSP), giving producers new genetic information to consider when selecting for calf health.
The new traits provide another piece of information to bring into breeding conversation while also raising practical questions: What exactly do the new PTAs measure? How much can genetics influence calf disease? And how should these evaluations fit alongside the management practices veterinarians already recommend?
New Evaluations Target Two Common Calf Diseases
The new DIA and RSP evaluations are based on producer-recorded calf health information collected through Dairy Herd Improvement programs and stored in the National Cooperator Database. CDCB and USDA’s Animal Genomics and Improvement Laboratory used those records to develop genetic evaluations for resistance to two of the most common health challenges affecting young calves.
“We have a lot of information for diarrhea and respiratory problems in calves. Those are the two most common things that calves encounter in their first year of life,” says Kristen Parker Gaddis, Ph.D., geneticist with CDCB, speaking on The CDCB CowCast.
The evaluations were developed using more than 768,000 respiratory disease records from animals between 3 and 365 days of age and more than 260,000 diarrhea records from calves between 3 and 60 days of age.
The new traits are expressed as predicted transmitting abilities (PTAs), which estimate the genetic difference an animal is expected to pass to its offspring. For DIA and RSP, PTAs are expressed in percentage points of resistance relative to the breed base. Higher values indicate greater expected genetic resistance in an animal’s offspring.
A PTA describes an animal’s expected genetic contribution to its offspring. It does not predict whether an individual calf will or will not develop disease.
The traits also have relatively low heritability. CDCB estimates DIA heritability at 2.6% and RSP heritability at 2.2%.
Those numbers put the role of genetics in context. Environmental and management factors account for much of the variation in calf disease outcomes, while the genetic component can be selected over time.
Why Add Calf Health to Genetic Selection?
The new evaluations provide information that is not fully captured by existing selection traits. Although DIA and RSP have relationships with existing measures of calf health, including calf livability, they capture additional genetic information that can now be incorporated into selection decisions.
“We’re getting new information from recording these calf health traits. They’re telling us something that we didn’t already know,” says John Cole, Ph.D., chief research and development officer at CDCB, speaking at their 2025 Industry Meeting.
The distinction could become increasingly relevant as producers consider the value of replacement heifers. Greater use of sexed semen and beef-on-dairy breeding has changed replacement strategies, making the health and survival of dairy replacements an important consideration.
“It’s really important that not only that we have these replacement calves, but we keep them in the herd and that they’re able to enter the milking stream when they’re needed,” says Cole. “These evaluations will help us produce healthier calves that will move from birth through the growth phase and then they will enter the milking stream at a higher rate than less healthy calves.”
For veterinarians, DIA and RSP can become part of conversations about replacement strategy and long-term herd health. They are intended to complement, rather than replace, calf management practices such as colostrum management, nutrition, housing, ventilation, vaccination and disease prevention.
Genetic Progress Will Take Time
The relatively low heritability of DIA and RSP also means these traits should be viewed as long-term selection tools rather than immediate solutions to calf disease.
“Genetic improvement is both cumulative and permanent. It will be slow, but genetics is really the long game,” says Parker Gaddis.
DIA and RSP are not tools for predicting whether a particular calf will become sick, nor are they substitutes for interventions that address immediate disease risk. Their potential value comes from gradually shifting the genetic makeup of future generations toward greater resistance.
What Happens to the New Traits Next?
The initial DIA and RSP evaluations are available for Holsteins and Jerseys. CDCB expects evaluations for additional breeds as more data become available. Reliability is also expected to increase as additional health records enter the National Cooperator Database.
The traits will not be incorporated into the lifetime merit indexes at their August launch. CDCB expects their inclusion to be considered during the next merit index revision. DIA and RSP can be considered independently as part of sire selection without assuming that either trait is already contributing to a bull’s Net Merit value.
The August Release Also Updates Fertility Evaluations
The calf health traits are part of a broader set of changes in the August evaluations. CDCB also revised Daughter Pregnancy Rate (DPR), Cow Conception Rate (CCR), Heifer Conception Rate (HCR) and Early First Calving (EFC), while introducing First Service to Conception (FSC).
The reproductive changes followed a two-year review prompted in part by changes in reproductive management since DPR was introduced in 2003. Synchronization programs, heat-detection technology, sexed and beef semen and changes in voluntary waiting periods have all changed how reproductive performance is managed and interpreted.
FSC provides a new measure of the genetic ability of an animal’s daughters to conceive in fewer days after first insemination. Unlike DPR, FSC is calculated independently of the voluntary waiting period, allowing it to focus on conception after breeding rather than when breeding begins.
For a deeper look at the reproductive evaluation changes and their effect on dairy merit calculations, see The New Math of Merit: How the August 2026 Evaluations are Modernizing Dairy Genetics.
The revised reproductive evaluations will affect the values of lifetime merit indexes such as Net Merit, Cheese Merit, Fluid Merit and Grazing Merit because the underlying PTA values have changed. The economic weighting assigned to individual traits within those indexes, however, has not changed.
More Health Traits Could Follow
The introduction of DIA and RSP also establishes a framework for adding additional calf health information as more records become available.
Continued producer participation will be important to that process. The new evaluations depend on health events being consistently recorded and transferred into the national database.
“We need folks to keep recording information in their on-farm management systems, and we need those data to keep flowing from the field through the DRPCs to the National Cooperators database,” says Cole.
As the database grows, the reliability of the calf health evaluations can improve and additional traits may become feasible.
For now, DIA and RSP give veterinarians and producers two new genetic measures to consider when evaluating future replacements. They do not change the fundamentals of calf health management. Instead, they add a longer-term selection strategy to the existing toolbox, giving today’s health records a role in shaping the disease resistance of tomorrow’s herd.
