Sounds almost like my first dog. Never heard of any issues at the track, but he just couldn't eat a total kibble diet. Nothing worked. Did all the unique proteins, no grain, yadda yadda. Tried tylan, flayl, probiotics, pumpkin, yougurt and something else. Finally put him on a raw diet (vet said we ran out of options). Started slow and he improved. He has been on a raw diet (no skin, no extra fat, no veggies, gizzards okay, liver no so much) and his poo is good 98% of the time. He did regain his lost weight and is a happy camper! It has been over 3 years now.