Whereas cattle today are often fed grains, the animals people ate throughout evolution roamed free and ate grass. Many studies have shown that the nutrients in beef can vary depending on what cows eat. Where beef is mass-produced, such as in the United States, cattle are usually fed grain.

Are most cows grain-fed?

All cattle are grass fed, but some cattle are fed a diet that includes corn for part of their lives. Grain-fed or “corn-fed” beef is the most widely produced type of beef in the United States. It is a product prized around the world for its highly-marbled cuts that are especially tender and juicy.

Why cows should not eat grain?

Grains can accumulate in an animal's intestines because they lack starch-digesting enzymes. Thus, a high-grain diet can promote an overgrowth of Clostridium perfringens, a bacterium associated with sudden death in feedlot cattle, Russell's article suggests.