I don't do goats but I show lambs so I will tell you what I do for them. You don't have to have a treadmill or anything fancy. Pick him up in between his front legs and walk him backwards every other day. Start at 40 seconds and eventually work up to 2+ minutes. That works his butt back loin muscle, every muscle the judge feels on it works that. Run him every day, I would say 600-1000 feet
So the best exercise for the goats seem to be getting them up in their hind legs. So I would get my die to stand on a block when eating. I hand her hay basket high so her has to put her foods on the little ledge. It gave her a huge butt. It you want to work on the shoulders you can get the horse halter and put it on like a dog harness. He look like hi might be a yearling size. Take some measurements. Get him on champion drive. They will amp up his growth and mussel. If you have a friend to help you then hold you goat on one side of a long road and got the friend shake his feed and unleash him. This worked great. And if you can get him to walk backwards. Sometimes with my lamb and my doe I would take a stand and collapse the back legs. This make a 45 ish degree. Put him on there 5 min a day and feed him some hay while up there to keep him happy.