I have (had) a flock of 13 chickens that were born June 1st of 2016. All have been healthy and happy until recently. They started laying around mid December. They were laying regularly until my 3 Welsummers quit laying about 2 months after they started. The other breeds are all still laying about an egg a day. Almost all of the hens lost a lot of feathers right around the time that the Welsummers quit laying... in a patch right at the base of their tail. I never saw mites or lice, but treated them with diatomaceous earth and some Blu-Kote spray (on different days, not close together). They still don't have their feathers back, but I haven't seen any worsening of the bare spots so I have left them alone. Tonight, one of the Welsummers came up dead. She had shown no signs of anything other than stopping laying a couple months ago. Since the entire breed had stopped laying and none of the other ones, I just figured that there was something seasonal with them... am I wrong? Is there something else I can or should do for the feather loss? Should I be concerned about the rest of my flock? They all appear happy now, but so did the dead one... right up until she died! She was not a very submissive or dominant bird, just kind of did her thing and didn't seem too bothered by the others. I need help!! I'm very confused by the death, lack of laying, and feather loss! Any advice is appreciated, thank you!!