Hi- I have 9 laying hens in my back yard. I got 4 initially, who are now about 7 months old. 1 Golden Comet, 2 Wyandottes and 1 Brahma. about 2 weeks ago, I bought 5 pullets- about 7/8 weeks old. They had been vaccinated. The chickens share a coop, but I had the babies sectioned off from my big girls. About 10 days ago, my Brahma and one Wyandotte started acting lethargic, tail drooping, yellow diarrhea. I separated them, took care of them, and they both appeared to recover after 2 days. I returned them to the other chickens. Now my other Wyandotte is showing the same symptoms, and the Brahma is sick again with even worse symptoms. I have them separated from the rest. I'm giving water soluble antibiotics. The sick ones won't eat and we have to force them to drink water. Not sure at all what to do from here. Any advice? Oh, it appears that the Brahma's irises are changing color to a brownish-red from golden.