I am new to chickens but have learned LOTS on BYC. I have a small flock of 12 chickens who were hatched August 1 and 3 laying hens who were hatched May 1. I obtained them all when my coop/run were complete in October. The 12 younger ones are farmyard mutts (standard size) and the three that started laying December 1 are black orpingtons. The last few days I've noticed one of the younger ones did not want to roost with the others and seemed to not move around much. It would stretch out a foot to the side a few times (not the usual straight back stretch) and seemed to not want to put weight on it. I thought it was only the right foot and it looked a little puffy to me. This morning it didn't come running to eat so I put some fodder next to it and it began eating. A few hours later when I went back to the coop to check for eggs, it was lying on its back with feet sticking up and head twisted behind. Before this I didn't notice anything like wry neck behavior. I touched a foot and it pulled away from my touch and blinked at me. I came in to research if there was anything I could do, then went out to check on it again. It hadn't moved and though it was still breathing, seemed pretty much done in. I hired a mercenary (my father-in-law) to dispatch the little thing because I couldn't stand it suffering and slowly freezing. Does anyone know what is wrong?? The rest of the chickens look fine. I don't heat my coop. It is a 9x11' converted (not insulated) playhouse with venting all along the eaves (22'). There are two doors and three windows that very little frost--no frost on the walls. The temp is single digits today. Their water was frozen this morning but I brought fresh and will do so again this afternoon before closing the pop-door. The roosts are 2x2 and are about 4.5 feet off the floor. I feed them fermented feed (a combination 1:1 of scratch and layer pellets) and fodder (alternating rye and wheat) and they have calcium and grit and I throw out scratch in their yard every day. The deceased's body felt warm but feet were very stiff, hard, and somewhat swollen. No sign of broken skin or discoloration (light yellow in color). The body didn't feel skinny or emaciated. Can anyone see something I should be doing differently or have any idea what the problem was? I would appreciate any advice! Thank you--here's a pic of them enjoying their fermented feed. The two black ones with combs are two of the three orps. This is the black one that died today.