I have 15 chickens, all mixed variety that have been totally fine for a long time (2 years plus) They were a variety of ages ranging from 3 to 6 months. They were all healthy, moving fine, clean water, food (they also range feed), great coup, etc. last night when they were put to bed, all 15 of them. They were all fine at 7:30 this morning EST. When I got home today at 4:00 pm 10 of them were dead in the pasture ... only one was laying on it's back with it's wings outstretched, most are on their sides. I also had two cayuga ducklings (under six months) that are also dead. Any ideas? They ducks and the chickens were never together. They only think they shared was food. I have one chicken that has not passed away cannot stand up and 5 that are perfectly fine. My vet is baffled. Let me know what you think. Thanks!