I agree with Terry – fecal exam for parasites, teeth checked and dental work if needed, check for ulcers. Then my hard keeper TBs do well with unlimited hay, and a twice daily mash of beet pulp, alfalfa pellets, and Purina Strategy. I supplement with Cosequin for joints and a vitamin/trace mineral supplement in addition to the salt/mineral block. If more calories are needed after that, then I add in stabilized ground flax. But check the medical things before you throw money at feed that he might not be utilizing well anyway!