with hatchlings its not to difficult to switch from either to rats. but i have had problems with sub adults that i've gotten that were on asf's. i call asf's bp crack because of it. I try to start all of my babies on rat pinkies/fuzzies depending on hatch weight that way i dont run into that issue. now if im having trouble getting one to take its first meal i'll try a mouse hopper a few times then asf's before assisting them in eating.