Hi, I'm new to the community. I've lurked on Backyard Chickens for a few years, and have gathered a lot of information, but I finally had to join when I saw this [relatively] recent post. And that's because we just addressed the same problem today ... and for the third time!
It was on one of our roosters that I first noticed one of these black, scaly "scabs." I picked him up, and felt something poking out of his chest. When I moved the feathers away, I saw this black protrusion of crusted matter, which had a radius of about half an inch, and it felt like it went under the skin. The edges of the "scab," however, felt loose and it didn't seem like the thing was attached underneath the skin either ... instead, it seemed like it was just buried in there. I assumed it was an ingrown feather.
Call me crazy, but I pulled it out! I got a little nervous when the matter seemed to get wider than the hole from which I was pulling it. The rooster, on the other hand, didn't seem to mind. So I finished pulling it out, and that was it! No blood. The rooster was fine and went on his merry way. And that was about eight months ago.
The matter, once out of his body, almost looked like a piece of cooked chicken with a rotten, black spot on it.
On the second chicken, the spot was also smallish--but directly in her ear! I pulled it out too, but there was a lot of fibrous pus type stuff I had to clean out separately. Again, the chicken seemed fine.
Recently, this third chicken started to limp. And the primary caregivers (my husband and father-in-law) of our chickens couldn't figure out what the problem was. (In our family, my "role" has become the chick-raiser, chicken doctor, and wound care specialist.) They told me she had some matted feathers, but couldn't find anything physically wrong with her foot or leg. So I took a look at her, moved the feathers away, and there was one of those black, scaly "scabs," and it was huge--this one had a radius of about two inches! As with the other chickens, I pulled it out. Again, it looked like a piece of cooked chicken with a giant rotten spot on it. And it stunk!
We hope that we can save Big Bird, but we might have to euthanize her. The bulk of this "scab" was just under her skin, and left a gaping hole, but it went deeper than the ones I've found before. There was another layer of infection (?) beneath the primary "scab," a hole that seems to go deep into her thigh muscle--and perhaps down to the bone. Even with this one, there was no bleeding, but I had cut the feathers around the area and perform wound care.
I'm disappointed because if I'd found this earlier, and removed it then, it would have spared her a lot of pain and discomfort.
Unfortunately, I still have no idea what this is. And I'm sorry I can't help you out with that, but I thought my experience might be beneficial in some way.