I think the issue is around the fact that there is absolutely NOTHING natural about this whole charade.
1. It is highly unlikely that a tiger would encounter a cow in a natural setting
2. Even if they did/do, the cow has far more of a change (irrespective of how slim this chance is) to escape from the tiger/s
3. There is simply no way a cow can escape if it is literally dumped into a tiger enclosure
4. The entire thing is completely manufactured for profit as there is absolutely no reason to do it otherwise. You don't see other zoos/conservation parks doing it, not least because of the ethical reasons/implications, but also because it's perfectly reasonable to keep tigers without resorting to such contrived, disgusting methods of upkeep.
5. It has nothing to do with whether the tourists feed them or not. I very much doubt the zoo keepers are going to let the tigers starve to death if no dull tourists cop up a few quid for a squirming creater
6. God knows what conditions these poor creatures are kept in before being thrown to the tigers - it is beyond questionable