Have you ask the seller or breeder if they had any die. A necropsy might help. Very spooky. Did you know if they were losing weight even thought eating. I had cases were torts were eating BUT not with vigger. If you kept weights maybe you can tell. I've also known the Alfalfa pellets (the dehydrated kind) can exspand in the gut when water is taken in. The Tort will dehydrate almost instantly. If you have worked with them for 50 yrs then you might have noticed if they were dehydrated looking suddenly. Very disribing to have a feeding animal die.This is all I could think of in my experence, but would be freeking too! Good luck and let us know what you find out. Vic