Gary Rogers is driving down a highway in Tennessee pointing out the dairy farms and cows that dot the landscape. He has a bit of data that a Northeast city dweller finds eye-opening: "All of the black and white cows around the world are related, and I don't mean 500 years ago," he says. In fact, today, most of the nine million dairy cows in the United States share just a handful of paternal grandfathers.
That has resulted in intense selection, and Rogers, a University of Tennessee dairy scientist, is worried about the potential downstream effects. "Selection always has to be balanced by what it does to inbreeding," says Rogers. "That was one of the things that got me interested in the health issues of dairy cows. No one else is really looking at it, and it has deteriorated in the last 15 to 20 years." (For more on changes ...
