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.
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.
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.
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.
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.
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.
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
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.
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.