Banging the gavel… “Look at this adjusted weaning weight boys…he’s a whopper!”
Okay, but what are you as the bull buyer actually taking home in the genetic package?
Let’s dive into a Weaning Weight (WW) EPD.
Angus defines WW EPD as “expressed in pounds, is a predictor of a sire’s ability to transmit weaning growth to his progeny compared to that of other sires.”
ASA/IGS keeps it pretty simple: “Reported as the difference in pounds of progeny weaning weight. Higher values are more favorable.”
So let’s boil that down.
WW EPD is predicting differences in the direct genetic potential for growth -> weaning that an animal is expected to transmit to its offspring.
Let’s say we’re comparing two bulls:
Bull A = +90 WW
Bull B = +70 WW
That’s a 20-pound difference. If those bulls are mated to females within a group, we’d expect Bull A’s calves to average approximately 20 pounds heavier at weaning than Bull B’s calves. This is not saying that every calf sired by Bull A will outweigh every calf by Bull B by 20 pounds, but on the average for a group, this would be the predicted difference.
So why can’t I just look at the bull’s actual or adjusted WW?
Adjusted WW helps us make a fairer comparison of the phenotype that was measured. WW EPD is trying to predict the direct genetic difference and provide more insight into what that animal is expected to pass along to offspring.
Seedstock producers…here’s where our reporting matters again (starting to see a theme?!)
Get the calves across the scale at some point between 160 and 250 days of age (according to BIF guidelines), ideally with the contemporary group weighed on the same day. A weaning contemporary group should represent calves of similar age and that have had an equal opportunity to perform: same management, location, feed/pasture, etc. If calves have been managed differently, they need to be denoted appropriately.
Remember our saying…when in doubt, split it out or at least raise the question to someone who likes to nerd out on this type of information, explain the situation and listen to their advice.
Lastly, weigh AND report the whole group. The 850-pound calf right off the cow is impressive, but his performance becomes much more informative when we know what his group mates (contemporaries) did under the same opportunity.
Commercial producers…if you sell calves at weaning, pounds obviously matter. More pounds getting loaded on a truck can be a good thing (depending on the slide). That’s one reason WW deserves a place in the selection conversation. BUT…here’s where I’m going to sound like a broken record: The goal isn’t automatically selecting for extreme. It’s finding your optimum. Selection for growth needs to be a consideration, but if you’re retaining replacements, we also need to think about the cow we’re building behind those pounds too. Mature cow size, nutrient requirements, maternal production, fertility and whether that female fits the environment she’s going to be expected to work in. That’s why I like using percentile rank to establish a range that fits our breeding objective rather than simply chasing the biggest weaning weight numbers in the catalog.
Key Takeaways:
Don’t get so blown out of the bleachers by the weaning weight printed in the catalog that you forget to ask what you’re actually buying and bringing home, the genetic potential matters.
Actual WW tells us what hit the scale. Adjusted WW helps put that phenotype on a more even playing field. And the WW EPD helps predict the direct genetic difference in weaning growth an animal is expected to pass along to its offspring. Use all the information available and find the WW percentile range that fits your marketing endpoint, honors your cow herd expectations and makes the most sense based upon available resources.
Do you remember our MILK discussion? WW is the calf’s direct genetic potential for growth to weaning. MILK is the maternal contribution to pre-weaning growth expressed through the daughters’ calves. Related pieces of the weaning weight puzzle, but they aren’t predicting the same thing and shouldn’t be used interchangeably.
Disclaimer: I’m not a geneticist. The information above is compiled from breed association resources and translated into practical terms based on my understanding and application of these tools.
