[Gothmog]

You're probably right, Eldar14, but the animals I thought of was not the usual zoo-animals and their keepers, but animals that of some reason has been left without parents and are raised by an animal keeper, not in a zoo together with other lions (or whatever the animal is). Besides, there are few animals that hunt humans for food. Polar bears are the only land living animal that do that. In other cases, wild animals attack to defend themself, their offspring or their own area.

To keep the animals, or in this case orcs, away from strerssing situations might be necessary. But then an orc isn't comparable with an animal; the orcs have a more advanced brain and can think for themselves. If they don't want to adapt to the elven/human world, then they won't. But if they have a wish to leave the life of their kin behind, then I still think it's possible.