Quote from ByLoSellHi:
Bison (buffalo) is remarkably lower in saturated fat and cholesterol than beef.
The same trend holds true for most 'wild' varieties of animal proteins: Ostrich, elk, venison, kangaroo - all much lower in saturated fat and cholesterol than beef.
You can get necessary trace minerals such as zinc, along with iron and B6, in these other 'wild' red meats, also. More importantly, you can get necessary amino acids - that one has trouble obtaining from anything other than 'red' meat, from these 'game' meats.
Cows and sheep have been bred to be fatty, with less and less striated muscle tissue than wilder, leaner animals. Bison have quite a bit of striated muscle - they still must be able to run quickly and suddenly if the herd is threatened by predators, or if they have to quickly run through treacherous waters filled with aggressive predators (i.e. crocodiles).
Beef cows and sheep (lamb) (cows - mostly hereford and angus) are now docile, as they are protected by ranchers, and have been bred free of the need to react and move suddenly and quickly when threatened. The ranchers protect them with fencing, and even when grazing, accompany them with firearms and herding dogs that protect the flock.