Hi everyone, a mystery illness is killing off my birds. I have a mixed flock ranging from 3 mos to 1 year. Ill go into the coop, find a ruffled, unthrifty, huddled bird almost weightless, with a slight gurgle and no other symptoms, within 24 hours of coming indoors for R&R the gurgling worsens, accompanied by gasping, then dead. I have treated with tylan IM and Oral, but it doesn't seem to help at all. I have also tried treating as coxi (weight loss got me thinking), but sulfa doesn't help either. It seems to affect the smaller, less robust birds. No discharge, no sneezing, no bubbly eyes, no foul smell. What on earth?? I keep my coop clean and dry, I don't do deep litter this time of year. I'm in canada so it's always a little chilly (-2,-3 max) in the coop but I have heat lamps (several) to keep the water from freezing and some nice cuddle spots too. I have a commercial exhaust fan constantly on, blowing air out of the coop. The indoor air is clear, dry, no hint of ammonia. What on earth is killing my birds??