Quote from Istril
And they don't buy beef (according to the wiki), but they buy leather and products made with leather. God I'm going to have to throw away SO much beef.
Or you could, you know, eat the beef. It's the best food item in the game (except golden apples and carrots) except for how much trouble it is to breed for it. If you're going to be breeding and killing cows anyway, why not keep their delicious meats?