Beef is the clean flesh derived from slaughtered cows and is limited to that part of the striate muscle which is skeletal or that which is found in the tongue, in the diaphragm, in the heart, or in the esophagus; with or without the accompanying and overlying fat and the portions of the skin, sinew, nerve, and blood vessels which normally accompany the flesh. (AAFCO, 2003) Not all beef is the same - do your research to find out if the beef in the food you have chosen for your pet is not fed any antibiotics or growth hormones. Beef is a good, digestible source of protein, though some pets are allergic to it.