I occasionally get chickens that seem to suddenly become ill and are unable to walk. They don't have the one leg in front, the other in back, but rather just unable to make much use of the legs at all. They eat and drink. The ones who have become ill will linger for a long time. The are coop chickens - the free range ones do not seem to get the problem. I have been dosing with Sulmet, Wazine wormer, antibiotics but nothing has worked. I would really love to know what this problem is and how to treat it. Thank you.