I had a pair of game bantams that WERE allergic to the pine bedding. I'd given them antibiotics, medicated chick starter, and treats. Someone suggested allergies. I changed them to sand bedding, and within 2 days the sneezes were gone! Then, when I'd let them run around, if they got near the pine shavings in the compost heap/garden they'd come back with the clear runny nose and sneezes on occasion- but appeared healthy the whole time.
But recently, I bought 3 hens that WERE SICK Yellow nasal drainage that crusts over the nostril, and one wheezing and 'coughing' turned out to be MG. (mycoplasma galli-something). I was really glad I'd quarantined them in my garage from the get go, and had never let them near my coop. Especially since this is apparently able to be transmitted to the eggs also! They went to the state for testing, which was how I found out. It was a one way ticket, but better losing $18 for the three hens, than infecting my whole flock. (The state paid for it d/t worries for AI which was negative).
