Why not feed them a complete diet? If you can't keep them don't try. Cat food is horrible for them, it has way too much salt, fat, and meat. If you want to save money combine your order with a friend's and buy from a local mill... You're question about how much is too much, I wouldn't give them any. It is unhealthy for them, if you won't eat unhealthy things that are no where near a proper diet why would you give them that?