I came across this in another thread and not sure if it was already explored as a possibility. https://www.merckvetmanual.com/poultry/mycoplasmosis/mycoplasma-synoviae-infection-in-poultry#:~:text=The%20more%20severely%20affected%20birds,of%201%25%E2%80%9310%25.
I wasn't aware that it could...
It sounds heart wrenching. Seems like you're trying everything possible. I don't know much about Marek's, but obviously seems like something systemic in the flock. I'm sure you considered consulting a vet, maybe that was mentioned somewhere, but I know avian vets or even just vets that will see...
Reading this post now and wondering if you learned anything new or have any updates? I have one hen who also suddenly has difficulty walking, but she is a spindly leghorn mix and I suspect a sprain from rough mating, so hoping it's not nutrition related. Can't find any signs of bumblefoot so...