:I would recommend against using the younger rats, simply because they are higher in fat and if fat really does cause problems with hogs, you don't want to compound the problem. Older mice have higher calcium content (ossified bones) but this may not have much relavance to hognoses.
:Like Andy said, I've been feeding mostly mice and some minnows to a couple of easterns for over 10 yrs now. Consider yourself lucky by having some that will eat for you!
My larger juveniles take large fuzzie mice, and my adult EHNs take adult mice.