I have several different breeds of laying hens and have NEVER had any problem with disease. I lost a hen 2 months ago to what seemed respiratory and because I panicked I ran all birds through 7 day Duramycin treatment. Lost a bird yesterday whom was completely fine the day before. Our weather is nutty, 68 then 40s then 20. I have had a few birds coughing or sneezing off and on winter. What's going on??? Any help greatly appreciated. They get fresh water daily, veggies, and are on 20% protein crumbles since going through molt recently.