I am not a breeder nor do I play one on TV.

I only live with one. That being said, I can only tell you what I've observed from him. I believe he starts with mice because for their size, there's a whole lot more action from them, further enticing the snake. Now, I recently bought a baby Burm from him and at the time, he had a couple of meals in him so when I got him, he had not been switched yet. A few days later, I tried to feed him a hopper because from what I understood, that's what he'd been on. Well... he didn't want anything to do with it. As a result, I now have a couple of fugitives. Out of frustration, I fed him a rat pinkie/fuzzy and he took it. I agree. Rats are preferable and if the baby is big enough for a ray pinkie, he should start out with rays. Its much easier when they are babies than when they ate sub-adult like Mick the mouse eater Irian Jaya.