They weren't born that way: Both female and male Holsteins naturally grow horns. But on farms, the horns of dairy calves are often removed (an unpleasant process for the animals), so that the cattle won't pose a threat to one another, or the farmworkers handling them.

Now, a team of researchers at the University of California-Davis has come up with another way to remove the horns. By swapping in a gene from the naturally hornless (polled) Angus breed, the researchers created hornless Holsteins that are born that way. Is the polled Holstein a new type of cow — a genetically modified organism? Or are researchers just speeding up the breeding process?

"To me, this is precision breeding as much as anything," says Alison Van Eenennaam, an animal geneticist at UC Davis who led the research. "We're able to introduce a desired genetic variant [into Holsteins] very precisely, without affecting any of the other genetics that makes them great milk-producing animals."