This Genetics Company Is Editing Horns Off Milk Cows

Geneticist Scott Fahrenkrug knows a callipyge when he sees one. The term, which means “beautiful buttocks” in Greek, is often used by livestock breeders to describe a mutation that causes an animal’s post­erior to grow to twice the average size for its species, meaning more juicy, flavorful meat.

Fahrenkrug saw his first callipyge in the 1990s, when he was working at an obscure U.S. Department of Agriculture facility charged with finding ways to predict which individual animals could be bred to produce the meatiest offspring. “Genetic improvement faster—that really was always the objective,” he recalls. Seeing the USDA’s back-heavy sheep, and some unusually well-muscled bulls, led him to start thinking about shortcuts, like the advanced tools he’d seen used to tweak fly and worm genes in his grad school lab. “I knew that once you know the mutation and you understand the biology,” he says, “you can exactly produce the outcome.”