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Despite All The New Selection Tools, Calf Birthweight Still Rules?

calving ease selection tips

Many years ago, when I was what Earl Butz once described as a lump of clay, ready to be molded, I was a student worker with the cow herd at the institution of higher learning I was attending. Back then, the folks who were trying to mold all us lumps into something they thought would be useful to the beef industry were chasing all the growth genetics they could find. Bigger is better seemed to be the mantra.

And, within reason, it is. However, back in those dark ages, all we had to work with was actual performance data—EPDs were just coming on the scene and a bull’s actual birthweight, 205-day adjusted weight, and yearling weight were the performance data that ruled.

As a result, calving season became a “teachable moment” for both the molders and the moldees. I can’t recall the numbers, but I can vividly recall pulling a lot of calves that year. And not just in the heifers, although they were the epicenter of the wreck—we pulled plenty of calves from the mature cows as well.

Among the many lessons we all learned was that just because a bull had a light birthweight didn’t necessarily mean he was an easy-calving bull.

Fast forward more years than I’m going to admit to. We’ve come a long way in our understanding of genetics and genetic interactions in those years, and not only do we have very solid EPDs to guide our decisions, but a growing understanding of genomics.

It was thus with eyebrows raised high that I looked at the results of a recent survey that BEEF magazine did of its readers. You’ll read a more complete rundown of the survey results in the February magazine, but the answers to one question caught my attention as they sent me on a not-so-memorable trip down memory lane.

Here are the top five responses when we asked “Which of the following information do you require to purchase a bull?”:

  • Actual birthweight—72.9%
  • Birthweight EPD—68.6%
  • Calving Ease-Direct EPD—58.5%
  • Actual weaning weight—55.3%
  • Weaning weight EPD—52.9%

What raised my eyebrows in this data was the reliance on a bull’s actual birthweight and weaning weight in the decision-making process of whether or not a buyer raises a hand to bid on a bull. Here’s why.

“Of the genetic variation in calving ease, birthweight only describes 47%,” says Bob Weaber, Kansas State University Extension cow-calf specialist and one of a handful of my go-to guys when I have a question on genetics, which is often. “So you leave the other half on the table when you just focus on birthweight. We know birthweight genetics play a role in calving ease, but birthweight alone doesn’t describe all the genetic variation in calving ease. Other factors like calf shape and muscularity play a role too.”

Weaber says it’s important to also recognize that genetics don’t control all the variation in calving ease or dystocia. Environmental factors such as cow nutrition during gestation, among many others, play a big role in a calf’s ability to express its genetic potential. “The heritability for calving ease in Angus is 0.2, which means 20% of the variation in phenotype (or a calf’s actual performance) is under additive control; 80% is environmental,” Weaber says. “Birthweight has a heritability of 0.42 in Angus. So about 42% is genetic control, 58% is environmental.”

In spite of the fact that birthweight is more heritable than calving ease, Weaber recommends that if you’re looking for an easy-calving bull, focus on the calving ease EPD. That’s because it combines multiple traits, including the bull’s (or its sire’s) calving ease score, among other things, as well as its actual birthweight.

For cow-calf producers, calving ease is the economically relevant trait. Birthweight is an indicator trait. Birthweight provides some information on calving ease, but birthweight alone doesn’t directly generate revenue or incur costs. “Calving difficulty or dystocia is what gets you in your hip pocket,” Weaber says.

The other consideration with selecting for birthweight only is that it has a fairly strong correlation with other growth traits, Weaber says. Reducing the birthweight may lead to decreased performance at weaning and yearling.


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Thus, he recommends that if you’re selecting bulls to use on first-calf heifers, look for bulls with a calving ease EPD in the top 20% of the breed. In most breeds, it is relatively easy to find calving ease bulls with desirable levels of growth; bulls that beat the genetic antagonism between calving ease and growth, he adds.

I understand why actual birthweight and weaning weight are attractive indicators. Those are numbers you can wrap your brain around. They mean something because they’re real-world. EPDs and genomics, on the other hand, are not numbers that intuitively make sense without a deeper understanding of what they mean. But in the highly complicated world of genetics, focusing on a bull’s actual performance data alone can lead you into a wreck if you’re not careful, as we learned those many years ago.

“Some people fall into the trap that birthweight has a higher heritability than calving ease, so if you select on birthweight, you make more progress,” Weaber says. “Well, you’ll make more progress on birthweight; you won’t make more progress on calving ease. So put the selection pressure on calving ease. You’ll sleep better during calving season and your heifers will appreciate your astute use of genetic prediction tools.”

What are your thoughts on this discussion? Which selection traits are most important in your program and why? Leave your thoughts in the comments section below.


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