Duramycin10 is on the weak side for coryza. If you are treating coryza, sulfadimethoxine is probably the best antibiotic or Sulmet second, from what I have read.
Infectious Coryza and chickens, Its like a severe cold. - Page 5
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Edited by rlcrow - 10/26/14 at 3:00pm
16 died but were there some remaining or was that all there were? You say the guy you got the sick chickens from stopped whose outbreak? Yours or did his chickens get sick? I have read in multiple places that you should leave the pen and grounds vacant for three months before repopulating with new birds. I would see about sending one to be tested to find out for sure since this is the second time you have had to deal with this. Unfortunately respiratory issues may seem to get better but they are actually ticking time bombs that come back again later. You can't cure them. If you bought birds that had a respiratory issue from someone then you brought it to your place with the birds.
- Poop Inspector