Just grasping at possibilities here...is there a chance that the food could be moldy?
Also, Speckledhen lost Hawkeye from using something with benzocaine in it. Is anyone who is handling the chicks using any medication on their hands? Once I read what happened to Hawkeye, and learned how sensitive birds are to that drug, I made a mental note to never have it on my hands when handling chicks. I know it's a longshot...