I purchased a new Igloo chicken coop with a run area and new adolescent chickens. I separated them from my exciting flock.. I believe due to overcrowding and lack of keeping coop clean, the chickens developed respiratory illness.. They have responded well to antibiotics and kept them away from my other chickens 2 weeks after antibiotic finished. However, I started letting them free range again and I am noticing respiratory symptoms in other birds. I hear a gurgle cough. The funny thing is these chickens are not lethargic. They eat well and lay eggs. Should worry about this cough?