Definitely! And you are lucky he is that easy to put weight on! All my appendixs have been hard keepers so consider yourself blessed! But I would follow Dr. Wagner’s advice and get your hay tested! I feed Buckeye Gro N Win which is a ration balancer that has all the vitamins/ minerals/protein my horse needs but in a very very low cal feed! A ration balancer might be perfect for your guy if he can keep his weight with just hay!