He was approximately 5 months, but I think the Brahmas mature more slowly than other breeds. Also, my flock is free range they have access to acres of grazing land, so nutrition shouldn't be a concern I don't think.
I'm suspecting limberneck (botulism). It is caused by toxins or poisons by a germ called Clostridium Botulinum. After a couple hours of a chicken ingesting spoiled food, decaying meat, or maggots containing the toxin, the signs can be nervousness, weakness, sleepy, loss of appetite, difficulty swallowing, progressive paralysis of the neck, wings, and legs. During the final stages the bird may lay on the ground, neck stretched out and unable to lift it off the ground, or away from its body. The feathers become loose and pull out easily.
The only treatment I know of for it is 1 tablespoon of Epsom Salts in a half cup of water as a mixed solution. It has to be gradually tube fed, or syringe fed, down the bird's throat twice a day for 2-3 days. The best thing to do is prevent it by not allowing access to moist, spoiled feed or meats. A clean yard should be maintained, (no rotting debris, stagnant water, etc.)
If botulism isn't the case, it could be neurological or something viral like LT (Laryngotracheitis). There is much respiratory distress with LT though, and bloody mucous from the mouth is commonly seen. If you can get the bird bagged and in the refrigerator, call up one of the local NPIP labs and ask them if they can do a necropsy. It does no good for me to give you the link since the USDA site is down due to the supposed "government shutdown". I hope that helps.
. Thank you for the advice.
