I had 6 chickens all from the same place die within 2 months of each other. One Wyandotte started with a cough. Then the others started mild cough. Gave antibiotics in water for 2 weeks in the course of those two weeks all died but two. Then another died about 2 weeks later and today another died. No other symptoms except a dAy or two before they died they became very lethargic. Treated with vet rx and antibiotics (yellow granular) in water. Any thoughts? I have five other chickens and one we thought was becoming lethargic so we isolated it gave it antibiotics and apple cider vinegar in water. Seems to be better. Cleaned out the coop the other chickens were in and bleached the inside and all feeders and waterers. Put another flock in. Any thoughts on why they died. I feel like we are doing everything we know to do but are experiencing a lot of death and it is discouraging. Any advice is appreciated.