There's a bug in Planet Zoo where Zookeeper simply refuse to give food to the animals. This obviously has huge consequences, because the animals will first become very unhappy, and eventually they will die from starvation.
Keep in mind that while some players are getting the bug where the zookeepers won't feed the animals, other users have done something wrong that prevents the zookeepers from actually doing their job. Have you made sure that the staff have access to a Staff Room? If not, that might be why they refuse to feed the animals.
Some users will experience that the zookeepers refuse to feed the animals no matter what, and unfortunately this is a known bug tied to pathfinding in the game. Basically the zookeepers get stuck trying to find a path to get into the enclosure and the feeding area. At the current time, there is simply nothing you can do to fix the bug easily, but there are some workarounds that you can use until the bug is fixed in a patch.
The only method to fix this bug is to change the layout of the enclosure to force the zookeepers to use another path to get to the feeding area. This will usually solve the bug, but it requires some effort. If it does not fix it, you might not have made a big enough change for the pathing to be changed.