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Most U.S. dairy cows are descended from just 2 bulls


Unlike most dairy cows in America, which are descended from just two bulls, this cow at Pennsylvania State University has a different ancestor: She is the daughter of a bull that lived decades ago, called University of Minnesota Cuthbert. The bull's frozen semen was preserved by the U.S. Agriculture Department.

Dan Charles/NPR

Chad Dechow, a geneticist at Pennsylvania State University who studies dairy cows, is explaining how all of America's cows ended up so similar to each other.

He brings up a website on his computer. "This is the company Select Sires," he says. It's one of just a few companies in the United States that sells semen from bulls for the purpose of artificially inseminating dairy cows.

Dechow chooses the lineup of Holstein bulls. This is the breed that dominates the dairy business. They're the black-and-white animals that give a lot of milk.

Dairy farmers can go to this online catalog and pick a bull, and the company will ship doses of semen to impregnate their cows. "There's one bull — we figure he has well over a quarter-million daughters," Dechow says.

The companies rank their bulls based on how much milk their daughters have produced. Dechow picks one from the top of the list, a bull named Frazzled. "His daughters are predicted to produce 2,150 pounds more milk than daughters of the average bull," he says, reading from the website.   MORE>>>>>