Half my flock has Coryza...should I cull the “healthy” half as well?

[Raeganmh02]

This is a bit of a long post, I apologize. I have another thread concerning my infected birds, but now I am concerned about what to do with the “healthy” half. So far the healthy birds consist of 8-month-old Dominiques and a few 4 year old road island reds. The ones getting sick so far are the older 4 year olds. At the moment, 7 are sick and 13 remain okey (so far). I intend to cull the sick ones as hard as it may be, but I wonder if the others might have it “mildly”. Is this possible? Can a bird show mild to no symptoms and still have the infection? Some of them have some puffiness around the eye (could be peck injuries, scabs near the eye are visible). Some are acting a little depressed due to them molting. I want what is best for my future flock, so if culling the entire flock is what I need to do, I will. At the moment, I have been listening inside the coop at night for labored breathing, and checking their breath for the bad Oder. So far, none are showing any strong symptoms. It has been 6 days since the last infected bird was detected. Instead of the whole flock getting infected fairly quickly, they are slowly getting it one by one. There was a two week gap when the first ones came down with it, and I thought the rest were good..then suddenly another bird started showing symptoms. I have been cleaning out the coop well and disinfecting their waters and feeders. They are pasture-range chickens. I have been giving them all apple cider vinegar, garlic, oregano oil, and cinnamon (not sure if all those could “stump” symptoms). I guess my questions boil down to:“Can my chickens have Coryza and not show visible symptoms?” And, “should I just go ahead and cull the whole flock to be safe?”
I know it’s a lot of detail, I’m trying to figure out all the knots since I’ve never had to deal with anything like this before. Many thanks!!!

 

[casportpony]

Did you have them tested for Coryza?

 

[Raeganmh02]

Yes, I did. It came back positive. I’ve talked to others and I've done a lot of thinking, and I’ve come to the conclusion of culling them all. Some more are showing symptoms, and I’m pretty sure they are all carriers now. I hate it, I had a few I really liked and an amazing rooster in that flock, but I’m wanting to continue to add some new ones to the flock and I don’t want to deal with all of it forever. At first I was thinking of hatching offspring from them since they have such neat genetics for colored eggs, but now I’m starting to think they have MG as well. It’s been rough but I’ve definitely learned some good lessons in this. I’ll know how to protect my future flock.