In one of the flocks I am looking after, I had a young chicken (3 months old) die within several hours. He was perfectly fine in the evening, went to sleep happy, next morning his legs were paralyzed and his beak was full of mucous. I assumed some kind of yeast (we are in fall and very wet season here) and gave him Nystatine. It didn't help, he became more and more paralyzed and died within a few hours. Today I noticed a hen in the same flock, who wasn't drinking water, I checked her and she had mucous in the beak. Is this yeast or what else should I look for?