The problem with cows, is that they do not efficiently metabolize grass. Yes, they *can* eat grass, but usually as a last resort. Other plants make them grow much faster and fatter, like alfalfa (a high protein clover) and of course corn. Cows that are grass-fed have very tough meat with very little (or no) marbling.
Buffalo on the other hand can eat and metabolize grass very well. But the downside is that buffalo take seven years to become fully grown. I believe a cow takes about 18 months. Buffalo also have a much higher amount of omega-3 fatty acids than cows, due to their diet of grasses rather than grains.
