Shortly after I got my girls, I noticed they were sneezing & had runny noses. I called the farm where I got them from, and was advised that it was an allergy to the hay they had in the nesting boxes, and to swap it for straw. I did this but there was no improvement, and the girls started to blow bubbles from their noses, and open their beaks to breathe. I took them to the vet who diagnoses a severe respiratory infection and prescribed Tylan soluble for 5 days. After 5 days they were still sneezing, so I continued the dosage for another 5 days at which point it seemed to clear up. I disinfected the coop and run thoroughly. Since then, both girls have gone through further episodes of sneezing. They both have permanently dirty nostrils, as if there is a bit of moisture still there for the mud to stick to. They both still open their beaks to breathe sometimes, but seem to be able to breathe fine without opening them too. Both are energetic, eat well, lay daily without fail, have bright red combs & wattles and no other signs of illness. Their chests do not rattle or wheeze. I have wormed them for gape worm and they regularly have apple cider vinegar or poultry tonic. The first time I redosed them with antibiotics, but it seems to have little to no effect. I've kept a stock to use should they ever appear to worsen, but I don't really want to keep medicating them indefinitely. I've read up on RTIs in chickens and understand that once infected, they stay for life. Is this persistent sneezing just an indicator of this? Do you think the mouth-breathing and sneezing could just be habit? Any insight would be very welcome.