Buster that is rough. It is hard to see a good friend having trouble like that. If I may suggest regular controled exercise.I always run my dogs beside my bike. You can just tie the leash to the seat post and that will control the speed and distance the dog travels. I have never met the dog that gets the exercise that they need on their own. Start off with a mile for the first four days and then two miles for the next week. You can play with the distance as you see fit according to how he is doing.
Remember, a dog is an extremely effecient runner, so what may seem like a long distance to you, is not for him. A person can not jog far enough or fast enough to properly exercise a dog. This last thing, I believe whole heartedly; If he is no longer able to have a good quality of life( run, play, HUNT) as a dog would see it, and that is not in people terms, put him down. Too many people are selfish with their pets and keep them around for themselves while the pet withers away.
P.S. Do not breed this animal, we have enough poorly bred animals now. Animals generally pass along their poorest traits and genetic problems when people breed them. He will more than likely pass this problem along as well.
Good luck with this problem, I have been down this road before.
Qaz