I've never felt comfortable with the thought of horses being used for glue, pet food, and human food, even though I know in some countries it's been done for generations. Feeding them to lions... really upsets me. They're not even natural prey for African cats! Ox, yeah, I could see that. Even things like antelope would be okay. Personally, giving large cats a chance to actually hunt in capitivity probably alleviates a lot of stress on the cats. It's a brilliant idea to keep them stimulated and try to recreate wild life for them.
I remember watching this one episode of Emergency Vets, when the hippy dude (his name excapes me at the moment) was treating a sick rabbit. The rabbit's owner had stolen it from her boyfriends house because it was dinner for the bf's snake. The bf thought that the snake had eaten it, and so the snake was essentially starved for a short while. Dr. Fitsgerald (remembered it!) stated that someone has to think of the preditor. "They need to eat,too." With some animals, such as snakes, live food is needed, even though that live food is cute and cuddly.