I don't bother to train them to eat any specific thing. They seem happy enough to eat without being encouraged one way or another.
Generally, this is true. It's only when you make the pets contribute and get a job that eating is a problem. Often they come home exhausted and hungry, and choose to sleep while I get messages about them starving to death. You wake them up, and instead of eating, they go back to sleep. Doing a Command - - Eat is necessary then.