Hen still having raspy breathing after being treated with Tylan 50

As far as the sick bird goes...this is part of the long-term implications of  CRD.  It is a chronic, life-long condition.  She will likely need to be put on a more powerful antibiotic like Baytril, but I believe (could be wrong) the only way to gain access to Baytril is through a vet.

You need to decide what you want to do from here.  I would start by having her euthanized and tested.  I, personally, have a zero tolerance policy for respiratory illnesses.  The cost is too great in the long run- both financially and emotionally.  An infected flock takes all the joy out of poultry keeping.

I would recommend you have the whole flock tested.  Most of the illnesses that fall under the CRD tag are very contagious.  If she spent any time at all with any other members of your "healthy flock" they are likely only asymptomatic  carriers at the moment, but at the first sign of stress they will get ill.

I am sorry.

It may.  Any stressor from this point forward has the potential to impact their health.  It also won't help.  Once they get CRD they have it for life.  That's why testing is so important.

Seriously.  I would love to get some different blood into my flock, but any local swaps are just too much risk.

I am sorry, and good luck with the rest of them.

Today one of my hens is displaying the same symptoms you described.  We've only had chickens for 2 1/2 years, and this is our first sick one.  I have her isolated.  I was doing research and came across Gapeworm.  She is not breathing with her mouth open, but is making the rasping sounds and the gurgling.  She also doesn't want to drink or eat and consequently is not pooping.  I don't believe in going to extreme measures or expenses unless of course it is our favorite one. :)  I need advise.  How long do I give her to see if this clears up on its own?  If I need to put her down, I just as soon do it sooner than later.    

What vaccinations? There are VERY few backyard people who even know there is a vaccination for CRD, much less who do it. The most common vaccination is for Marek's Disease and another one used is for coccidiosis, both given at hatch. Neither have any effect on CRD.

It may not even be CRD. Could be a virus, in which case, antibiotics won't touch it. With most chicken diseases of the respiratory nature, the bird is always contagious, even if the symptoms go away.

Sorry for your experience. No swaps, not ever, no flea markets, no started birds from anyone, not even those I trust, is my policy. All are hatched here from folks I know who cull automatically for any disease symptoms.

eirwin, you need to start your own thread for this.