as a quater bull he'll be very 'fine' anyway......I have had a similar problem recently with one of bitches who has lost loads of wieght and is pissing back passage.....yet hungry as a hog, and still bright.
I am currently trying to build the bitch back up, and have changed diet.......re wormed, and feeding twice dialy...so we'll see how she gets on......
worst case senario is it could be an underlying symptom of bowel disease or some intestinal parasite..........
hope you get him sorted