Short Wave - Most U.S. Dairy Cows Come From 2 Bulls. That's Not Good.

Episode Date: November 12, 2019

NPR science correspondent Dan Charles explains why most of the dairy cows in America are descended from just two bulls, creating a lack of genetic diversity that can lead to health problems. He also visits a lab at Penn State University where scientists are trying to change that. Follow reporter/host Emily Kwong on Twitter @emilykwong1234. Email the show at [e-mail]. See pcm.adswizz.com for information about our collection and use of personal data for sponsorship and to manage your podcast sponsorship preferences.NPR Privacy Policy

You're listening to Shortwave from NPR. Emily Kwong here, your host when Maddie Safaya is off for the day. And I'm here with NPR science correspondent, Dan Charles. Hi, Emily. Hey, Dan. So today you've brought us a story about cows. Right. It started a few months ago.

I saw an article in an online publication called Undark. This article asserted that all of the Holstein cows, which is the breed that's most of the dairy cows in the country, that they were all descended from exactly two bulls. Two, two bowls? And I said to myself, this cannot be true. So you went off to find out if this was true or not. And what did you find?

It is true. Okay. There are almost nine million dairy cows in this country. And apparently almost all of them are descended from exactly two bulls, which if you want to get technical about it, means in this entire population of bulls, there are only two Y chromosomes represented. That's of all the bulls that produce practically all the dairy cows in this country. But that might actually be a problem.

So today on the show, why it's an issue that cows are all so genetically similar and what scientists are trying to do about it. Okay, Dan, this discovery that 99% of America's dairy cows are from two bulls, Where did it come from? Came from a guy at Penn State University, a professor of animal science named Chad Deccal. Decao? Like cow? Yeah, so it's close, but it's, you know, there's cow in there, but we try not to emphasize it. Chad is a super friendly guy.

I grew up on a dairy farm in upstate New York. And he told me, if you want to understand this, you've got to understand how dairy cows reproduce these days. So it goes to its computer, opens up a website. This is the company Selects Sires. This is a company that sells semen from bulls. So if we just look at their Holstein lineup, for instance. So Holstein cattle are the black and white ones, which give a lot of milk. That's the breed that dominates the dairy business.

It says loading America's finest bowls there on the screen. That's right. We're looking on the screen at this big list of bulls, dozens of them. So if I was a dairy farmer, I would go to this website or one like it. I'd pick a bowl from this list, and the company would ship doses of semen to me that I would use to impregnate my dairy cows. In fact, there's one bull who we figure he has well over a quarter million daughters. Oh, my goodness. And how do people decide which cow semen to purchase?

So the companies, they rank their bulls from sort of top to bottom, based on the amount of milk, that their daughters produce. So this is a bull named Frazzled. His daughters are predicted to produce 2,158 pounds more milk than daughters of the average bowl. So the farmers will pay extra, for instance, for semen from top-ranked bulls because they figure the daughters will give them more money down the road, produce more milk. And the companies that are breeding these bulls, they keep trying to make their bowls ever better. So they mate their top bowls with the most productive cows.

They keep selecting the same families over and over again. So here's where we get to the discovery, right? Chad Deco got to thinking about this and wondering with all this selection going on, are we ending up with bulls and cows that are more and more genetically similar? And lo and behold, everything goes back to two bowls born in the 1950s and 60s. And their names? Their names were Round Oak Ragapple Elevation. in Pawnee Farm, our Linda Chief.

Those are some fancy sounding cow names. Don't you love the names? These two bulls, they lived in the 1950s and 1960s when the system of artificial insemination really got going. Their descendants, these bulls, the few hundred bulls that are in those catalogs, they are not all genetically identical. They still had lots of different mothers and grandmothers. But there is a larger point here, and that is the system of large-scale,

artificial insemination that we're talking about with farmers picking the top-rated bulls. It has made the entire dairy herd less genetically diverse. Oh, no. And that has actually led to some health problems. We've lost genetic variation. Some of that genetic variation was garbage that we didn't want to begin with, but some of it was valuable stuff that will be gone. And Chad Deccal is actually doing this really interesting experiment to kind of get a sense of that. Okay.

Walk me through it. He located some old semen from bulls. that were alive decades ago. Okay. Because you see, the U.S. Department of Agriculture keeps samples of old bull semen, keeps it in deep freeze storage in a vault in Fort Collins, Colorado. As you do. And Chad selected two bulls for this experiment.

They have names too. There was University of Minnesota Cuthbert and Zimmerman All-Star Pilot. What is with these names, Dan? He used their semen to impregnate some modern cows. They gave birth. And now if you go to a barn at Penn State University, you can see what amounts to lost pieces of the Holstein family tree come to life. Right here is our old genetic lineage, this is number 2869. She doesn't look any different, does she?

Well, you'll notice if you look kind of over her back, you see that cow on her left. It's a little bit more bony over her back. Yeah, absolutely. So she definitely carries more body condition, a little bit fatter. So this is really interesting because keeping more fat is a genetic trait that dairy farmers for a long time didn't want in their dairy cows. They thought the ideal cow was a skinny one because that cow was turning all the feed she ate into milk and not fat. So farmers would choose bulls that produce daughters that were skinny like that. We've kind of selected for tall, thin cows, and that's a really bad combination.

They're infertile, they're unhealthy, so we need to get away from them. that? Is that because we've been essentially inbreeding cows? We have been inbreeding cows. There's actually a technical measure of the amount of inbreeding that you can kind of measure over time with cows, and it has gone up. And so deckhouse thinking, maybe the frozen semen from those long-forgotten heirloom bulls can actually bring back valuable genes that went missing, like those genes for extra body fat, or maybe genes to tolerate warmer temperatures. there's a hitch though. Well, this is a question, isn't it? I mean, it sort of seems like it'd be a good idea. Generally, if farmers did, you know, sort of get a little more genetic diversity into their herds.

But there's not a lot of incentive to? There's no incentive to. And in fact, there's some disincentive because profit margins on farms are so tight right now that you can't afford to make a mistake. And if you use an old bull and it has lousy dogs, and you've got to milk those daughters, your hurt's going to be a little less profitable than your neighbor, and you're going to be out of business. So there's, at least that's the perceived risk that people would avoid taking. We want to use the best genetics because we want to be efficient and be able

to make a living. So how are his experimental cows at that barn in Penn State doing? He says they're doing pretty well so far. There are three of them that they're milking and keeping records on. And two of the three are producing at least as much milk as the industry average. And for him, you know, average is actually good. And again, two of the three are a little fat, fatter than your classic Holstein modern cow. Dan, not only do you report so thoroughly on the dairy industry, but you also grew up on a dairy farm. That's true. I did. What does this discovery, if anything, how does it make you think differently about this? animal upon which this industry is built.

I think for me it's this interesting thing that I never really thought about. But it's also not completely surprising because, you know, you realize even though, you know, a cow is an animal, you know, it's kind of nature. But you also realize that it's very much a manipulated creature through breeding over many years. And so it's like most of agriculture, actually. It's part nature, but very much a human creation. Dan Charles, you're the Food and Agriculture correspondent on NPR's Science Desk, and we're glad to have you. Nice to be here.

Hey, if you've been enjoying Shortwave and all the bite-sized science stories, we are bringing you on the daily. Do us a solid and rate and review the show in Apple Podcasts. When you do, it helps the show get recommended to other science nerds out there who haven't heard about us yet, but whose lives will be changed forever by it. I'm Emily Kwong. Thanks for listening to Shortwave from NPR.