Just consider me another vote to up the size of your prey. Most cornsnakes will put on a growth spurt once they're moved up to whatever the next size is...
A good rule of thumb is that corns can safely handle prey up to 1.5 times their widest point.
Older, closer to adult mice have better nutrients than younger, juvenile mice. Rats of the same size as mice generally have more of everything (protien, calcium, fat)... I don't have the nutrition info on hand, but I know atleast one person on this forum does... Once my corns are big enough to take adult mice, I switch them over to rats of same size. And while corns can do just fine on adult-mouse-sized items, again, most corns will put on growth spurts when offered larger items.
I also reduce the feeding frequency once a snake is on hoppers or so... those get fed once a week. Once a snake is on rat pups (roughly the size of adult mice), I'll slow down to about every week and a half... sometimes every two weeks. I have a few corns that eat small rats (and are capable of eating medium rats without difficulty).
Anyway, goodluck with your corn.
-Kat
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"You keep WHAT in your freezer?"
"Mice. And rats. If that bothers you, I can call them 'cows' instead."