Vet RX....
That's pretty much my one-word answer. It's a symptom-treating remedy for lots of illnesses like this, but it also treats mites.
I'm about to post to my own thread that I had recently about this, but long-story short, I've got some type of respiratory illness going around my flock. I introduced a single roo to the flock out of four chicks that I purchased from another hatchery. Three of those chicks died. The roo seemed to be okay, so I kinda added him in with the others. They stayed separated by a single piece of netting.
BIG MISTAKE. Whatever the three young chicks died from, the older one (who SEEMED to be okay) passed on to the rest of my flock. After the third chick died, I took her body to the vet and he just confirmed it was a bacterial respiratory infection. Their death isn't from the germ itself, but every single one of them died from suffocation - they had mucus build-up SO BAD that it literally cut their breathing completely off. The older chick passed it to a bantam roo and hen. I noticed their problems when I heard the roo's crowing was hoarse, and as I attempted to catch him to bring him inside, I heard the hen's rough breathing too. The treatment I mentioned above cleared it up (although I also used duramycin injections). It has only been about a week since they went back outside.
But I've got a large-fowl ameraucana (my favorite out of my entire flock) sitting on towels on my bed right now with a heat lamp on her. It sounds like she's constantly making a "coo" sound simply because the breathing is SO LOUD! As she breathes, I can actually hear the mucus moving around in her throat with a rough rumble-type sound.
The hatchery that I got the chicks from told me a day later that he found out his chicks had mites (but has denied his chickens were ill in any other way). He mentioned treating it with VetRX, and that's how I found out it worked for the respiratory infection. The key is getting it INTO the chicken. I use an eyedropper for the large-fowl birds and squirt some INSIDE of their nostrils (don't worry, they aren't using it to breathe anyway) as well as some into their mouth for them to swallow. And just for the mite issue, I also put a couple of drops on their backs, right at the base of the neck.
The older chick that passed it on to my flock ended up developing the symptoms soon after, and I brought him back in and gave him the drops - WITHOUT the antibiotics. He has cleared up now.
So whatever this is, it is HIGHLY contagious. This guy's chicks gave it to my flock, and now it's going around the entire flock. But it moves slowly, because they are all developing the issues one by one. And it doesn't really make them lethargic, aside from being unable to breathe. They eat and drink just fine. They even play, forage, and BREED just fine. It's all in the lungs, throat, and nose. That's it. But be prepared to treat your entire flock. As soon as one gets it, they all will.
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If you choose to add the antibiotic like I did, the injection kind of Duramycin is available at
Tractor Supply Company. They also have a powder form you can mix with their water, but for free-range chickens that can access water from ponds, streams, and rain puddles, I'd stick with the injection. The powder form makes the water bitter, so they avoid it if they can. They only need about 1/10th cc/mL for bantams, and about twice as much for large fowl. The easiest way to dose them is actually a diabetic's syringe/needle. 1/10th of a cc is the same as 10 UNITS on a diabetic syringe (20 units for large fowl).
You only need to inject it once. No follow-up SHOULD be needed. And if you use an antibiotic, be prepared to give them yogurt (with live, active cultures) to help replace the beneficial bacteria in their digestive system, starting about a week after you treat them.
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