It seems to be related to the noun " encastelure" which is a veterinary term for a disease of horses' hooves caused by the horse standing for too long in water or urine. Sounds horrible. I found this in a French veterinary text online, and of course , it did not give the English equivalent. (It's not foot rot because I looked that up also. That is "le pietin" with an acute accent which my current keyboard will not allow me to add. )