Goodnight Linda. Hope your kiddo gets better. I was off trying to track down my #2son, 16 now with a driver license. Haven't heard from him since this afternoon, he had a robotics meeting tonight which is across town, in the dark!! I'm too old for all this teen driving stuff. Not much hair left to turn white!
Anyway, he just called and on the way home. sigh
We can call it a tie!
I just did a quick search. You get the best results from searching your address.
I was wondering, but hard to say from a pic. I can't remember the specific vitamin, but what granny said sounds right. Don't think it will hurt them to try anyway.
Are the tail feathers breaking off? I had a SL Wyandotte that started having weird problems with her feathers, they were all broken up. Went on for over a year. I thought she needed to molt to set her straight, but it never happened. She eventually weakened and died and I didn't find out until later that she probably had QUILL MITES.

You never see them. They live inside the feathers and you treat with ivermectin to kill them. Pesticide has to be in the blood to kill them as they feed.
If you see him getting worse, try an ivermectin dose.