Unless you are a small hobby farm, you’re not putting your cows out on pasture alone to raise them for meat. Most grasses are deficient in one or more vital nutrients that the cows need to grow. Most cows today are fed TMR (Total Mixed Rations). These are diets carefully mixed with different grasses, grains, hays, and mineral supplements. There are different metabolic diseases that cows can get when eating diets deficient in different nutrients. Cows that are sick don’t want to eat, and cows that don’t eat don’t grow. To a farmer, that’s like burning money.