Hello, I have a flock of 15 hens. The 4 oldest are two year old black sexlink. Two of them have sneezing and coughing. One of them smells bad. The other 11 are mixed breeds: 5 RIR, 3 Barnevelder. These were purchased 13 weeks ago from a local feed store that ordered them from a hatchery. None of the younger ones are sick. However... About a month ago, I went to a different feed store and bought 3 new Buffs close in age to our other now 13 week hens. I believe these birds sickened my older hens. I took 2 of them back separatley because it was obvious they weren't right. We were advised to use Duramycin-10. We did a full course of that. And after a week of no change, started a second course. Yesterday we went to a different feed store that suggest we use Sulmet. I am so confused! Can you advise me what to do about my flock? Treat all of them the same or only the obviously sick ones? For the 2 sick birds we took back: One of them died and the feed store told us today the other seems to be getting better. She said she is giving her B1 in her water.