I've been having ongoing respiratory issues with my chickens. It started with some chicks I got several months ago, they all died (less one), and it's gone through my flock. Symptoms have included coughing and sneezing. With the younger chicks that died due to this had raspy and open mouth breathing It's not been as severe with the adults. It seemed to clear up for the most part but I've still been hearing periodic coughs/sneezes. Today I found two deceased in the coop. One when I picked her up had white drainage/discharge from her nose and mouth. Does anyone have suggestions on what this may be and how to get rid of it? Any advice would be appreciated!