We are losing a hen every few months to the same pattern. Upon falling ill they've all died in less than 12 hours. I've seen many questions about similar symptoms, but we haven't found the resolution. Hope someone can help. We have 12 hens of various ages and breeds, no roosters, in a backyard coop. They eat an organic pellet feed, occasional greens/kitchen scraps, and oysters shells or grit mix. They don't receive any medications. Approximately every six months we come across a hen -different ages and breeds- unable to walk. At this point they are usually lethargic, barely able to raise their heads, but sometimes they will be bright eyed, thirsty, not hungry, and yet still unable to move outside of a feeble flap. They are not doing the awkward Marek's walk/splay and both legs seem to be affected at the same time. We see the hens every day, so it always seems like a sudden onset. The crops feel normal. Their vents are usually clean unless they've progressed and then we find them messy with watery, gritty poo. Vents are usually pulsing and the abdomens feel swollen so we have suspected egg binding, but we haven't ever seen them in the penguin waddle stage - only laying down where they're at as if nesting, but without leg strength. We do the warm soak treatment, feed calcium (usually watery yogurt since they will drink some, but not eat), and in other cases have felt in the vent per other instructions. There is always watery poo of various colors (green, yellow, and light brown with some white, often frothy or gritty looking), no eggs are ever felt or passed. We isolate the sick hens as soon as we find them, but have never had one survive. They curl up and die within hours. The rest of the hens appear fine for months, until it happens again regardless of season or weather. We don't have a local vet that cares for hens and haven't found anything that follows this pattern in the books or online. Advice is greatly appreciated.