Why does my rooster look like this?

[Goosebaby]

Metzer has a directory of avian vets, maybe there’s one near enough to you who might have an idea.
https://www.metzerfarms.com/Veterinarians.cfm

 

[Eggcessive]

His neck looks affected, as in wry neck (crook neck torticolis.) That can be neurological, and sometimes vitamin E and thiamine (B1) along with a small amount of scrambled egg for selenium can be tried to see if it helps. Since he has lost weight, make sure that he is getting to food and water, and not being kept from it. Worming him with Valbazen or SafeGuard Liquid Goat Wormer should not hurt.