Hi Karen, FWIW my Cushings/IR gelding George will get sheath swelling
when the sugars in his diet start to rise. The swelling is never
brought down by exercise, however, only tightening his diet. And the
results take time to show. In your case, sounds more like a lymphatic-
type issue as it responds immediately to exercise. Maybe he needs more
turnout time?

Lavinia, George and Nappi