This is a new development. Looked at the neck of this chicken yesterday and didn't see anything. Today we see a skin sack with something hard in it at the base of the neck.
Is it a bone growing? Or maybe... could it be an in-grown feather? Any advice appreciated. Photo attached.
Could be an ingrown feather, or a foreign body that's become embedded and encapsulated, or a tumor. Any of those three are fairly common. Doubt it's a bone no matter how hard it feels. Could be an insect/spider bite, they're often good for making cysts.
Out of curiosity, why were you looking at its neck before? I take it there is something overall wrong with the chicken?
Today the spot is about the same, maybe a little larger.
To answer the question about if there is anything else wrong, we noticed mites and have treated all the chickens by clipping some of the feathers and applying vaseline. We have also dusted with wood ash. This seems to have worked but now we notice this lump. The mites were focused mainly around the vent but we also found them around the neck... hence the extra caution leading to finding this cyst or something.
Since we don't know what the cyst or lump is, best to leave it, probably. Some things can become a problem if cut into.
If you feel so inclined, you could tie a thread around it to cut off circulation and let it drop off, but cutting into it might not be the best idea. It's up to you.
Some people cut or lance any lump they find, but there's some cancers, viruses and bacteria that if cut into can spread throughout the system and make serious, even fatal, problems, whereas if just left or not cut into they will remain dormant. The body has isolated that lump for a reason, so releasing its contents into the bloodstream by cutting into it is something I wouldn't do just in case, personally.
It should be fine, but 'should be' isn't a guarantee. Removing it without cutting it open is better, and once it's off the bird you can cut it open and see what's inside, if you want.