The four calving traits calculated by CDCB went through a base change, and these updates are taking effect with August 2025 proofs. Here’s what you need to know about the calving trait base change.
What is the new base for the calving traits?
Table 1 shows the average PTA for each of the four calving traits across active AI bulls, comparing the new base versus the previous base.
How do these averages relate to difficult calvings and stillbirths on farm?
There are fewer difficult calving’s on dairy farms across the US today than there were five years ago. The new phenotypic base for sire calving ease is 1.36%. This number is the average frequency of difficult calvings in first-lactation cows where the calf being born is sired by a bull born in 2020. This new phenotypic base is lower than the previous base of 2.29%, which was calculated using bulls born in 2015.
What contributes to the improvement in calving traits?
We can credit a combination of genetics and management with the improved values for the calving ease and stillbirth traits. While genetics for calving traits has improved significantly, this shift is also attributed to the increased use of sexed and beef semen throughout the US, as well as improved maternity management on many dairy farms.
Why was the base for calving traits updated separately from the other traits?
The main US genetic base change took place in April 2025. When CDCB calculated the calving traits base change at that time, they noticed unexpected results, which led them to revisit the calculations to confirm. After much testing, they confirmed the results, which are now being published with August proofs.
Did calving trait values improve for all breeds?
For the Holstein breed, the calving trait values are listed above.
For the Jersey breed, calving traits are not calculated because there is a lower incidence of dystocia and stillbirths within the breed.
For the Brown Swiss breed, the average values for calving ease and stillbirths have gone up, which means there are more cases of dystocia and more stillborn calves today than there were five years ago.
Where does the data come from to calculate calving ease and stillbirth traits?
Calving traits are calculated using calving data recorded on farm. That data is processed at a Dairy Records Processing Center and then shared with the National Cooperator Database. As a refresher, here is how the five-point calving ease scale is defined on farm.
Calving Ease: Scale of 1 to 5 as reported by producers
- Quick, easy birth with no assistance
- Over two hours in labor, but no assistance
- Minimum assistance, but no calving difficulty
- Used obstetrical chains
- Extremely difficult birth that required a mechanical puller
For genetic evaluations, calving ease scores of 4 and 5 are combined as the measure of dystocia. Herds that report only calving ease scores of 1 are excluded from genetic evaluations because it’s assumed as a sign of poor data quality in most cases.
Stillbirth: PTAs rely on a scale of 1 to 3 that is applied to event categories. For genetic evaluations, scores of 2 and 3 are combined to account for the category of stillborn calves.
- Live calf
- Calf born dead
- Calf born alive, but died within 48 hours
What should I do with this information?
- If you are having challenges with difficult births or stillborn calves, then you may want to consider using bulls with lower values for calving ease or stillbirths. You may also want to consider an audit of your maternity area for any opportunities to improve your dystocia rates that way.
- If you do not see higher than average levels of dystocia or stillbirths on your farm, then calving ease and stillbirths are likely not the genetic traits that will make the most sense to include in your genetic plan.
- If you select bulls based on NM$, please know that the combination of the four calving traits are included in NM$ at a total weight of 3% of the index.
Where can I find more information on these traits?
For more information, please speak with your trusted Alta advisor or review a technical document published by The Council on Dairy Cattle Breeding with more details about the calving traits, which you can access HERE.
