Linds, I am very much a believer and watching the fat content in amphibian and reptile eaters. But I do have to add that thus far there has been no documented case which shows sufficient evidence to incriminate an all rodent diet. Although there have been a couple of snakes which died of fatty liver disease and were beinig fed an all rodent diet. Go figure.
All I'm saying is use your own judgement and proceed with caution when feeding Natricines especially, an all rodent diet. Then again, there are some more tolerant such as most common garters. Just showing both sides of the coin.