What B vitamin was he talking about?
I couldn't find any reputable sources (i.e. college, government, or research websites) that said freezing destroys a significant amount of B vitamins in rodents.
I also couldn't find any reputable sources that said anything about the importance of B vitamins in snake diets. Most I could find was that in garter snakes you need to be careful about feeding exclusively fish because that will lead to a vitamin B1 deficiency.
If it really worries you, a light dusting of frozen prey with a nice multivitamin solves the problem.
Ta dah!
~jenny
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"We call them dumb animals, and so they are, for they cannot tell us how they feel, but they do not suffer less because they have no words."
- Anna Sewell (1820-1878)