US, Canada & the Americas

From just two bulls, 9 million US dairy cows

From just two bulls, 9 million US dairy cows

There are more than 9 million dairy cows in the United States, and the vast majority of them are Holsteins, large bovines with distinctive black-and-white (sometimes red-and-white) markings. The amount of milk they produce is astonishing. So is their lineage. When researchers at the Pennsylvania State University looked closely at the male lines a few years ago, they discovered more than 99 percent of them can be traced back to one of two bulls, both born in the 1960s.