One of my more precocious girls grew lethargic and obviously did not feel well. Upon examination her crop was terribly swollen. I massaged her neck Very gently and she began to throw up the vile stuff. (Warning - they shake their heads and get it EVERYWHERE). I did that until it seemed there was not much left. Isolated her in a cage in the garage, she got kefir through a syringe every couple of hours. I left bread soaked in olive oil in her cage and when she began feeling better she did eat some. After 3 days of this routine her improvement was remarkable! She was her old spunky self and I returned her to the hen house and normal eating habits. When it reoccurred 6 months later, however, I had to go out of town and was unable to treat her. My hen sitter said he tried to follow instructions but she died. Not sure how stringent he was with the regiment, however. Hope to never see that illness again. I can't find much information about how to prevent it.