Cattle by design are ruminant animals, which means they have multi-compartmental stomachs intended to convert low quality plant protein into high quality feed. Ruminants have difficulty digesting cereal grain (corn, oats, etc.) because they lack a critical enzyme needed to metabolize starch. The simple act of feeding grain to cattle loads their bodies with fat and calories, robbing the meat of much of its nutritional value.
The meat from animals that have spent 150 days in a feedlot (a normal amount) where they are fed primarily grain has six times more fat than grass-finished meat, with a third of that being saturated fat. A six ounce steak from a grass-finished steer has 100 fewer calories than a six ounce steak from a grain-finished steer. By comparison, a grass-finished steer has nearly the same fat content as skinless chicken breast.