This has been an issue with him for the nine years that I have known him, and suddenly, it is resolved! He is like a normal horse, with just normal sheath cleaning needed. No smegma on his belly or legs at all, and the only thing I have changed is his diet. I changed his feed from Triple Crown (which I love) to a very high fat diet, based on Omegatin (20% fat) with oil, ground flax seed, black oil sunflower seeds, and supplements along with plenty of hay. He looks great, and smells even better! Could this diet really alter smegma production, or is it coincidence?