I have one who went off feed for 7 weeks, right after I got him. I had bought him as a rat eater, but he refused any offered, but as soon
as I gave him a mouse, BAMM in 1 second flat. Poor thing was starving by that point so I gave him 4 or 5, don't remember.
I've been giving him mice ever since. Being a male, I don't really care that he's a mouse eater, I have a steady supply.