I don't breed rats, but I did have a rat as a pet.

Don't give it anything plastic that it can chew. They can choke on it, also depending on the type of plastic it can be toxic.

At the typical big box pet stores, there are wood blocks that are safe. Don't give wood from the hardware store. It's treated, and toxic.

Be careful, or they'll no longer be feeder rats, but pet rats. This is one reason I prefer frozen...