I too have moral inhibititions about feeding rat, mostly because I used to show and breed them, and bonded with all my ratties. The issue has always been size, its just not feasable or healthy to feed 6 mice instead of one rat

If 6 mice were ground up whole and put in a sausage form to equal one large rat-- I would go for it. If it was proven to be just as good, I would totally switch off of rats