I have 6 hens. They are about 5-6 months old and have appeared to be in good health this past month. Today I found that one of them is completely listless, wont move on her own. When I pick her up she doesnt resist. Her breathing was laboured (not noisy or raspy, but more like she was taking big deep breaths that moved her whole body. Most noticable was that mucus was running from her mouth. Can anyone help diagnose please? I have isolated her, but wonder if I should cull her if she lives through the night? Any idea what might be ailing her and if there are any treatments? Thanks for your help. I'm a chicken newbie and this is my first illness.