Cow-Calf Commentary for Iowa Cattleman Magazine
By Randie Culbertson, Cow-Calf Extension Specialist
February 2026
Does genetics matter during calving?
Does genetics matter during calving? The short answer is yes, especially when considering heifers. The use of the wrong bull can lead to major train wrecks during calving. Cow nutrition, body condition, and management play critical roles for a successful calving season, but if the wrong bull is used, no level of good management is going to prevent calving issues. Reducing the incidences of dystocia can reduce labor needs, improve calf survival, and support quicker return to estrus for females after calving. Compared to cows, heifers tend to have higher incidences of dystocia, with calf size being the leading cause. Heifers are still growing, and their pelvic canal have not reached mature size. As a result, heifers are not capable of delivering the same size calf that a mature cow can. Incidences of dystocia in mature cows tend to be a malposition or deformed calf, and calf size is not usually the issue. The malpositioning of a calf is not predictable, and there are no tools to prevent it. Given that the majority of dystocia cases are a mismatch of heifer and calf size, focus is place on heifer development and bull selection. The strategic use of calving-related expected progeny differences (EPDs) provides operators with a genetic tool to select the appropriate bull for use on heifers to reduce the incidence of dystocia.
Three EPDs are relevant for improving calving outcomes: calving ease direct (CED), calving ease maternal (CEM), and birth weight (BW).
- Calving ease direct is defined as the likelihood that a bull’s calves will be born unassisted when he is bred to first-calf heifers. Higher CED values indicate fewer calving difficulties and a higher proportion of unassisted births. When selecting bulls for first-calf heifers, the CED should be considered since heifers are at greater risk for dystocia. The term "direct" for EPDs refers to the measure of the bull's immediate (or direct) influence on the calf's genetic expression for the trait of interest, in this case, calving ease.
- Calving ease maternal predicts the calving ease of a bull’s daughters when they calve as first-calf heifers. When retaining replacement heifers, CEM should be considered alongside CED to reduce the incidence of calving difficulties in retained herd replacement heifers. The term "maternal" refers to the expression of the trait by daughters and predicts the genetic merit of these daughters when they express the trait of interest.
- Birth weight is often emphasized when selecting bulls for use on heifers and is solely a measure of the calf’s weight at birth. This trait does not account for other factors that could contribute to calving issues, such as calf body shape. While heavier calves are more likely to cause dystocia, heavy selection for decreased birth weights will result in smaller calves with lower weights recorded later in life (i.e., weaning and yearling).
Heritability is the proportion of a trait expression that is due to genetic variation. The higher the heritability, the greater the genetic influence on the trait. Lower heritabilities indicate a larger environmental impact on the trait. Low heritabilities DO NOT mean that genetic improvement cannot be achieved, but that genetic progress will be slower and would require more attention when selecting for it. Heritability is measured on a scale of 0 to 1, but in reality, it never reaches 1. A heritability of one would indicate no environmental influence, but we know that trait expression has some level of environmental influence. In practice, 0.7 is typically the highest heritability value we expect to see. Birth weight has a heritability of 0.20 to 0.50, depending on the group of cattle measured, and is considered low to moderately heritable. In comparison, heritabilities of CED are 0.10 to 0.20, which is considerably lower than those of BW. With lower heritabilities for CED, why select for CED?
The simple answer is that CED is the actual trait of interest. When it comes to calving, we want a healthy, live calf on the ground that was born unassisted. Birth weight is irrelevant, except that larger calves can create calving issues. As a result, birth weights are included in CED because of a strong genetic correlation.
Genetic correlation is defined as the measure of shared genetic influences between two different traits, indicating that genes affecting one trait also affect the other. In the case of CED and BW, the genetic correlation is typically reported between -0.4 and -0.8 (moderate to strong correlations). The negative correlation indicates that as one trait increases, the other trait decreases. In other words, as BW increases, CED decreases and vice versa. Because of this, genetic evaluations include birth weight as a correlated trait when estimating CED EPDs.
The moral of the story is to use CED, not BW, when selecting bulls for use on heifers! As mentioned before, calving ease is the actual trait of interest. When it comes to BW, we want calves that won’t cause calving issues due to size, but we also want calves that will have some weight on them when it comes time to wean. Using CED removes this dilemma since BW is already included in the EPD.
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