Cows across the world feed on different varieties of grains, typically corn in North America, while a small percentage eat grasses and forage. There is no such thing as a wild cow, meaning that every cow consumes a regulated diet according to the properties the rancher seeks to give the beef.
Because of the way cows digest their food through four different stomachs, different grains are processed through a cow's body in unique ways affecting its muscle growth and altering its flavor ever so slightly. The vast majority of cows in America eat a heavy amount of grains, specifically corn, after their first year. This gives the meat a favorable amount of fat marbling that translates to richer flavors and a more tender texture.
Grass-fed beef, on the other hand, comprises less than 3 percent of the market. These cows spend their entire lives from birth to butcher consuming grasses. The meat is considered to be healthier, as it has less saturated fat and more beta carotene and omega-3 fatty acids. The reduced amount of fat marbling tends to make grass-fed beef hard to prepare. It dries out quickly, rendering the meat chewy and stringy. Taste is a matter of preference, but in one culinary blind taste test, judges concluded that grain-fed and grass-fed beef both had their finer points and weakness.