First off, all zoo directors should be encouraging enrichment at their zoos. A fat, bored animal is nothing anyone wants to see.
Second, it might be a challenge for some zoos depending on costs and what species is bored. Some more poor zoos may not be able to keep all of their animals satisfied. Keeping an animal enriched can be as simple as having a naturalistic exhibit for some animals but may be extemely complicated for others. Something like a mouse might just need an interesting, natural exhibit with places to run around and hid (something most zoo exhibit have). A gorilla, however, needs lots of room, climbing structures, mind games, physical games, and would need hidden food for it to find (not to mention a social group). Big cats would need the same kind of enrichment. This leads into the problem people have with having extremely intelligent animals in captivity like Chimpanzees, cetaceans, and elephants.