So now I am freaking out. Does this mean that I have to separate the ones showing signs and only treat them, or treat the whole flock? What do I treat them with? I am quite sure this came from the breeder, who I just spoke to and she has had it happen to her birds before. Does this mean that every bird on her property has the potential to be a carrier? I find it hard to believe that a breeder could never sell any birds again
And this is the problem, unethical breeders who simply DON'T CARE about your flock. They have lots of $$$ tied up and rather than lose that, they treat to hide symptoms and sell carrier birds to unsuspecting folks like yourself. Also, if she admitted it's happened to her, she has a carrier disease in her flock. And no, she should NOT sell birds to anyone, knowing they are carriers of whatever, mycoplasmosis, coryza or whatever, but she probably does not want to cull, disinfect and start over because it hits her in the wallet. It's very common for this to happen, unfortunately. She's either unethical or ignorant about disease.
Snot is NOT normal. I've never, ever seen snot on a bird in my life here. None here have ever had contagious respiratory disease but, I am very,
very strict in what I do. I never buy birds from anyone, not even folks I do trust. All are hatched here or from breeders (real breeders, not propagators-anyone can call themselves a breeder, but most really aren't) who don't treat birds, they euthanize them if they show signs of contagious respiratory illness. If it can be determined that it is situational pneumonia or a fungal infection, those are not contagious and can be treated, but anything that causes actual snot would be more ominous.
Even if you treat those birds, they are never cured. They are carriers. You can't fix that once something like mycoplasmosis rears its ugly head. First thing everyone should do is quarantine newly purchased birds for at least 4-6 weeks, preferably longer. If signs like you describe show up during a quarantine, they should be culled, never added to your flock. That's the purpose of quarantine, though even quarantine is not perfect. I know of a lady who quarantined a rooster from an NPIP certified breeder for 3 months. He was a carrier of Infectious Laryngotracheitis and when the state tested her now ill flock, they came and culled all of her birds, that's how terrible that disease is, plus the other NPIP breeder she got him from is in hot water now. So, quarantine is good, but up to a point. I'd never skip it, though.
All that said, the only way to know for sure is have the state vet or another vet test a bird. That means if it dies or it is culled, refrigerate then get it to the lab by the following day if possible. Chickens begin to decompose very quickly.