I met Dr Blais 15 years ago and at that time he was feeding mainly on rodent,so I introduce rodent to my garter snake and for long it was their main food source .BY experience I don't give rodent anymore.Their is lot of probleme related .
DrBlais show me the difference between captive bred specimen with wild caught .I cant explain it in detail but most probleme occur at long term and over generation.
In captivity female garter snake have smaller litter than wild one with the same size,but when you fed mainly on rodent more chance of incidence.
Slugs,dead babies,deformation,just few babies looking good ,these are the most related problem with rodent or when use heating pad.
I give trout jellow and worms to my garter snake,But I know on what they fed on in the wild And I think that the best ,the only thing good with jellow and rodent is very easy to us to get this food .

I know everything is about food and UV lighting!!