Update--In case anyone else has this problem and freaks out like I did (and actually thinks to check the archives first!):::
The problem gradually phased out on it's own. I did note a definite hinderance to their growth because of this. Processing day is delayed now by at least another week...
Glenda --
Thanks for the good advice. I do restrict feed, but I do it 12 hours on, 12 hours off. (Hard to tell how much they'll consume day to day, since they grow really fast.)
I will try the probiotics since it certainly cannot hurt. I just wanted to be sure that they didn't need...
I have been all over the 'net and archives here trying to figure out what this is and if I need to do something about it--and what that might be. Now I've taken some pics and I am hoping somebody here can give me a definitive answer. Best I can tell from my research is that this is shed...