I started off with 7 buff orpington laying hens last year, they were doing great. Then one died and a couple months later another and another within 4 months or so we had lost 4 hens. The only sign was depression some weight loss and death within a week of the intial depression. Antibiotics and fluid therapy via lactated ringers and vitamins did nothing. I figured I just had gotten a weak batch of hatchery chickens as I have had chickens for years nothing like this has ever happened. I also keep bantam chickens directly on the other side of the fence with no issues. I just got a trio of Cuckoo Marans and moved them into the pen the buffs had lived in, after cleaning it all out, for three weeks the Marans were great, but all of the sudden I noticed one maran acting slightly depressed though she was still up and around. I found her dead the other day...... I want to figure out what is going on, is the pen contaminated, or coincidence? keeping in mind that right on the other side of the fence are living 5 or 6 bantam chicken who have been and stayed healthy the whole time.