In recent years, American milk has undergone a quiet transformation. The milk produced by our dairy cows has become creamier and more luscious as breakthroughs in cow genetics and nutrition have pushed the fat component of milk—also known as butterfat—to all-time highs. In 2000, the average dairy cow made 670 pounds of fat in her milk a year; today, she’s making 1,025 pounds. No single trait in dairy cows has improved as rapidly with genomic selection as fat, according to Chad Dechow, a dairy-