I came across this thread after starting one about similar issues one of my BR hens was having- we noticed last Friday that she was sneezing and then later was holding her head up, opening and closing her beak as if she was having some distress breathing. We removed her from the flock and it sounded like her brathing was full of fluid. We began treating her last Sat with antibiotics and today is Friday- she is eating very well and her poop looks very normal. I have heard her sneeze a couple of times but her breathing sounds fine now- we will continue treating for a full 10 days then keep her in isolation for another 5 before reintroducing her to the flock.
We picked up 3 Crested Polish from a friend that wanted to reduce their flock and one is acting very similar to the BR- went ahead and pulled her out of their coop to treat as well- odd as the crested are in a coop about 200 yds away and do not share anything in common- water, feed bedding comes from different sources..