I had snot beak (clear snot) and some coughing that didn't respond to duramycin in the H2O (full course, 800mg per day for 7 days), so I gave my whole flock Tylan 50 1cc once per day, sub-q for three days. All responded except for one hen- BO, year old- who still has crackly sounding breathing and snot. She was originally the sickest of the flock. Should I continue the Tylan with her or move on to a different treatment? Will Tylan keep working for a few days, and should I just wait? If different treatment, what should I do? Any advice is much appreciated.