I've got mine on senior and joint supplements. He'll gain weight if you make sure he's getting enough supplements to help him, and if you give him pain relievers if he needs them. Probiotics help, and so do daily dewormers. Soaked beet pulp and soaked alfalfa pellets have never helped mine, but I've seen it help out the oldies at the therapeutic riding center. Another thing that helps is a sup called balanced power.