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Humans can’t eat grass, but the meat we eat should come from animals that did.

Truth be told, we do eat a little bit of grass. Three-quarters of all human nutrition comes from wheat, rice and corn, all of which are grasses. But what we eat is actually their seeds, the dense package of complex carbohydrates that is the specialty of annual grasses. Perennial grasses, which are more common, pack a larger proportion of their energy in their roots, stems and leaves; the building block for these is cellulose. Humans cannot convert cellulose to protein, but cows, sheep and other ruminants can, thanks to the resident bacteria in their highly specialized fermentation tank of a stomach, known as a rumen.

Grass-fed beef, as its name implies, comes from animals that eat perennial grasses all their lives. In contrast, “Grain-fed” beef is what is most commonly sold in supermarkets. While all cattle are grass-fed at some point in their lives, conventionally raised cows spend the majority of their lives feeding on corn and other grains, typically in a confined feedlot.

So what’s the big deal? Why is it so important to choose grass-fed when buying meat? 1. Grass-fed animals don’t need the large quantities of antibiotics that feedlot cattle do.

Most beef cattle spend their short life in concentrated animal feeding operations (CAFOs), where a thousand or more head of steer are kept in close, concentrated conditions and fattened up for slaughter as quickly as possible. Since the 1950s it has become routine practice to add low levels of antibiotics to the feed or water of healthy poultry, cattle, and swine to promote faster growth and prevent infections that tend to occur when animals are housed in crowded, unsanitary conditions. The practice is now so common that according to the FDA, which regulates the use of antibiotics in food animals, 80 percent, or the lion share of antibiotics used in the United States, are used not in humans but in animals, and most of those – an estimated 83 percent -are given to healthy animals, not to treat the sick ones.