By: Adele Harty, SDSU Cow/Calf Field Specialist
Winter and spring is the time of year when cattle producers begin making their breeding decisions for the following summer. With that comes many bull sale catalogs and EPDs (Expected Progeny Difference) that need to be reviewed and analyzed to determine which sire is going to best meet the goals of the operation, and can sometimes become a daunting task. The key is to have goals identified and in writing to ensure that the sires that are purchased are going to move the genetics of the herd in the desired direction.
Calving ease is very often one of the most important factors to consider for bull buyers, but which number should be used: birth weight (BW) EPD, calving ease direct (CED) EPD, calving ease maternal (CEM) EPD or actual birth weight? Many cattle producers will say they look at all of these and base their decision on giving one area more weight than another, but is this the best approach to accomplish their goals?
Let’s look at the definitions of a few EPDs to help determine the best number to use. Calving Ease Direct (CED), is expressed as a difference in percentage of unassisted births, with a higher value indicating greater calving ease in first-calf heifers. It predicts the average difference in ease with which a sire's calves will be born when he is bred to first-calf heifers. Calving Ease Maternal (CEM), is expressed as a difference in percentage of unassisted births with a higher value indicating greater calving ease in first-calf daughters. It predicts the average ease with which a sire's daughters will calve as first-calf heifers when compared to daughters of other sires. Birth Weight EPD (BW), expressed in pounds, is a predictor of a sire's ability to transmit birth weight to his progeny compared to that of other sires. Actual birth weight is what the sire weighed at birth.
From review of the definitions, there are two of the EPDs that make the most sense, depending on the goals of the operation. For instance, if no replacement heifers are kept, then CED should be used alone to determine the sire that will result in the most unassisted births. If one of the goals of the operation is to keep females from this sire, then CEM also should be used to determine the sire that will have daughters who will be more likely to have unassisted births.
The BW EPD can be useful, but it doesn’t give us anything more than expected birthweight, where the CED and CEM take other factors into consideration along with BW to determine the best option. Birthweight alone doesn’t explain all the differences in calving ease between sires. If the goal is to select sires that are easier calving, using CED will be a more accurate tool. It is not a good idea to use actual BW either, as there are multiple factors in the environment that played a role in that sire’s own BW and there may be no relevance or correlation to their progeny.
So, as the bull buying season gets into full swing, be sure to use the numbers that are going to help reach your goals. If calving ease is important, evaluate CED and CEM (if heifers will be retained) and don’t worry about BW and actual BW.