We have so many tools available; we shouldn’t have to be teetering on the verge of creating a lot of overly light-birthweight calves in a mature cow herd in good health.
When comparing two bulls of the same breed for birthweight, take the difference between the two expected progeny difference (EPD) numbers for birthweight, which are expressed in pounds as the unit of measure. For example, if Bull A has a 2.0, and Bull B has a 3.5, then we can reasonably expect Bull A to sire calves 1.5 pounds lighter at birth on average when mated to similar cows.
We must remember this is based on an average, and even calving ease bulls can sire a calf that might seem to be unexpectedly large. The dam and the environment (nutrition) also make a significant contribution to the outcome of a calving event.
Calving ease EPDs are only intended for use in mating decisions regarding heifers. As referenced last month, the calving ease direct (CED) EPD incorporates both birthweight and calving ease scores collected by seedstock producers. CED is expressed as a difference in the percentage of unassisted births. This time, the higher value indicates greater calving ease in first-calf heifers.
To evaluate two bulls for CED, again take the difference of the two EPDs. In the form of the previous example, imaginary Bull A has a CED EPD of 12, and Bull B has a CED EPD of 6. From this information, we can reasonably expect Bull A should transmit 6 percent greater unassisted births on average in first-calf heifers, given all other factors are equal.
Another indicator of calving ease in some breed evaluations is CEM, or calving ease maternal. This one is not as commonly discussed, but it may be you have seen it and wondered what it means. CEM is a tool that can be used for sire selection of replacement females.
CEM is also expressed in a percentage of unassisted births. The daughters out of higher-valued bulls are expected to require less assistance at first delivery. These tools can help us stay on track. 
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Jason Duggin
- Beef Extension Specialist
- University of Georgia
- Email Jason Duggin
