*disclaimer, I am not a geneticist so the following breakdown is based upon experience and research of this EPD. For breed or herd specific questions please visit with your Association.
As producers across the country prepare to invest in their next set of herd bulls, here’s another EPD worth discussing. According to the Beef Magazine Cowherd Genetics Survey, 78% of commercial bull buyers report requiring or using actual BW when selecting bulls. I want it noted, actual BW is useful information, but in true Data Genie fashion, let’s go a step deeper into why we should also be learning about the BW EPD, rather than simply relying on the actual weight of that individual bull when he was born to make an investment decision.
First, a note from a few Associations on the BW EPD:
Angus defines BW EPD as: “expressed in pounds, is a predictor of a sire’s ability to transmit birth weight to his progeny compared to that of other sires.”
ASA/IGS defines it as: “Reported as the difference in pounds of calf birth weight. Desirable values are dependent upon management goals, however if selecting for reduced calving difficulty the appropriate EPD to use is CE.”
Here’s the distinction we want to host a conversation around:
An actual BW tells us = what the individual animal weighed when they were born
BW EPD tells us = the expected difference in birth weight between the calves of one bull compared to the calves of another bull, on average.
Let’s say we’re looking at two bulls in a sale catalog:
Bull A had a 92 lb actual BW
Bull B had a 78 lb actual BW
Which bull is predicted to sire lighter calves? The answer is, we don’t have enough information yet. What if Bull A was born to a mature cow in a contemporary group where calves averaged around 95 lb, while Bull B was born to a first-calf heifer group in a contemporary group that averaged around 72 lb. Now those individual birth weights have a little different context…don’t they?
Remember…an actual BW is a measured phenotype. It’s the result we observed on one animal and is influenced by both genetics and the environment/circumstances surrounding that individual calf.
The BW EPD is a genetic prediction. It takes the reported phenotype and puts it into context with additional information available through the genetic evaluation to help predict the genetic differences that individual animal has the ability to pass along to his offspring.
So…why does this matter to seedstock producers?
This is why reporting complete and accurate birth weights across the entire contemporary group is VERY important. A 90 lb calf may sound heavy to some when viewed by itself in isolation. But what if 90 lb is actually average or even on the lighter side within that contemporary group? Now that tells us something that the individual number does not.
By reporting the whole group, we’re giving the evaluation the opportunity to compare calves that had an equal opportunity to perform and better identify the genetic differences represented within that group. Maybe calves by Sire A averaged three pounds heavier than calves by Sire B when raised under similar conditions. That information, along with pedigree/relationship information, age-of-dam adjustments, genomic information (when available), and information coming from related animals and progeny, all contributes to the published BW EPD you see.
So…what does this mean to the commercial producer walking the pens at the bull sale?
Don’t throw out the actual BW. Just don’t let it be the sole decision maker or reason you take that bull home.
That 75 lb birth weight tells you what that bull weighed on the day he was born, under the circumstances in which he was raised. It doesn’t give you the full picture. It doesn’t tell you how the same sire’s other calves weighed. It doesn’t account for all the additional related animal, progeny and genomic information available to the evaluation. It would take you hours and access to data you don’t have to put the entire picture together. And let’s not even go into ET calves…
Takeaway: We leave valuable information on the table when we don’t compare potential sires using their BW EPDs. One more thing to note: if the question you actually need to know is “Which bull is more likely to sire calves born unassisted out of my heifers?” Then don’t stop at the BW EPD. Slide over to the Calving Ease Direct (CE) EPD. BW is associated with calving difficulty, but it IS NOT the same trait. If you’re selecting a bull to reduce calving difficulty, CE is of paramount importance.
So take this on your bull sale roadtrip:
Actual BW tells us what happened
BW EPD helps predict what he’ll pass along to offspring
CE helps predict the likelihood his calves will be born unassisted when mated to first-calf heifers
BW and CE are different pieces of information answering different questions. The more of those pieces we use, the better informed our selection decisions can be. If you have questions, comments or you’re enjoying these, drop us a note to let us know below.
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