Any tips on switching to rats?

[Fritzl]

Incidentally what's the reason for the change from mice to rats !!

I tried what i said I was going to do and it worked, she ate the rat.
Reason for change is alot of people recommend getting them on rats asap. Apparently rats have more nutritional value. Also when they are picky eaters its easier to give one larger meal than multiple. The pet shops mainly feed mice because its cheaper.