Rats are fine for adding diversity. I say as long they'll take it and you KNOW its not bad, throw everything at them you can. Since you really don't see MBD in snakes, I am sure that lack of a calcified skeleton is really a concern. I know that a geriatric E I took care of kept getting stopped up with mouse hair and chunks of urates. We had to switch her to hairless rat pinks although it really has only helped some.
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"I know the human being and fish can coexist peacefully."
Governor George W. Bush, Jr.
"Sometimes I think the surest sign that intelligent life exists elsewhere in the universe is that none of it has tried to contact us."
Calvin and Hobbes (Scientific Progress Goes 'Boink', 1991)