I always dread this question, brace yourself, bully sticks are made from beef tendons, and tendons often come from the the bull's penis.
Merrick Bully Sticks Dog Treats: 6, 9, 12'', Bulk, Free Shipping As I said before, I give these as a chewing aid, not a food. If your dog can eat a bully stick in one day, it's too soft and isn't helping clean the teeth.