I had a similar thing happen to a couple of chicks. And you know what I found???? They each had a little chip of the bedding in their throat!! And I have the good kind. Don't ask me right now, can't remember but it is the kind I have read here and at the feed store is the proper stuff for chicks. I managed to save the little chicks. I am starting to think maybe I will go back to straw.. I never had any trouble with it in years gone by.