I bought 10 pullets (vaccinated) last June and all seemed very healthy and grew fast! I lost one early on...found her on the coop floor with a broken neck....still haven't figured out how that happened. Everyone else was fine until late November. We had three days of 24 degree weather which is pretty unusual for Central Texas, but I kept replacing the frozen water with fresh, etc. Went out to check on them and noticed that one of the ladies had a very purple comb and seemed sluggish. Checked on her about 30 minutes later and she had laid an egg at the door to the run instead of in her nesting box. I really knew something was wrong when she let me pick her up! I brought her into the warm house and put her in a big box with food and water. Thirty minutes later she was gone. The next day, the same thing happened to another one of the girls and I lost her, too. I don't think it was the cold because I know chickens can handle much colder weather than that and it only happened to two of the 9 remaining hens. Then this week (70 degree weather), I noticed that one of the girls was just sitting out in the yard instead of scratching and running around like the others. She came in with the others at dusk and I watched her eat some pellets and drink some water then jump up on her perch in the coop. I did notice that she seems to have some labored breathing. Next morning when I let them out of the coop she ran out with the others acting like she was just fine. When I got home from work, she was dead. The others seem fine. I'm puzzled because none of the three I've lost has had any sort of symptom. No runny eyes or nose, etc. It's like they are fine and within just a couple of hours they are gone. I let them out of the run for about an hour in the late afternoon and didn't start doing this until November when they were 7 months old. Since it's obviously not something that is quickly wiping out the whole flock at the same time, I'm just really stumped. Could it be something they are getting into during their free range time? We haven't used any type of fire any control or any other pesticide back there since August (three months before they started their hour of free range).