You should try using Spurs. Another thing is things like corn oil, and alfalfa can give them more energy. Corn oil will also give them a shinier coat. You should look up more feed things with sugar. They will give him more energy, safetly and will also mostly have at least a few benefits in other areas as well. Another thing, and I know it sounds weird, is do Liberty, or trick training before you get on. This will stretch his neck, back, and joints so they are looser and will make him a little more comfortable, and will help strengthen your bond so he will want to work harder. Hope something helps!