With mine, if I recognize a reason for eating I let the parents live. My reasons have been recent tank moving, lack of water, or overcrowding. If I can't tell why it's happening (recently I had a trio that ate the head off of every baby produced), I cull the entire trio.
Your diet sounds fine. How many rats per tub? I've noticed a big increase with groups over 1.2. It's just odd if it happens a lot for you, although I'm sure you're doing fine. Some ASFs just are blood maniacs.