I brought a new hen home, and within days, 6 of my hens have gotten cold symptoms - lethargic, coughing, gurgling, not eating. I put them in a separate pen with heat lamp, put Duramycin in the drinking water, and have misted them several times daily with VetRx. I've ordered Oxine, but it's not here yet. They've been sick for a week now. I don't want them to suffer, but I love my hens and don't want to give up if there's hope of recovery. How long does chicken "flu" last, and what else can I do? Thanks!!