Many fictional worlds have their civilizations (usually the bad guys) ride some sort of carnivorous animal, usually something like a wolf or a creodont. Think something like the Wargs from Lord of the Rings, though this goes as far back as the Thracian Mares.
It has often been pointed out these kinds of mounts are very inefficient because it costs a lot more to feed an animal meat than keep an animal with a simpler, more cost-efficient diet like grass. We all know the real reason why these characters are riding carnivorous animals: because it's cool. But how could this be justified in-universe?
Assume for a moment a civilization has to make use of a carnivorous, vaguely creodont-like mammal as a mount or beast of burden like the Lord of the Rings Wargs. Say this is the only easily tamable animal that civilization has access to that can bear the rider's weight or something, with the other animals in the environment either being too small, too aggressive, not having the right body shape to bear loads, etc. What would be the most effective way to feed these animals?
It is okay if these animals are somewhat omnivorous or can be fed non-animal protein. I am more trying to figure out how to preserve the image of someone riding a carnivorous, wolf-like beast that can eat their targets if given a chance.
Mostly what I was wondering if there is some kind of protein rich food or way of storing animal protein that would make it (relatively) cost-efficient to feed these animals, assuming these animals are technically omnivores but are still primarily predators.