The things I know you can do for a dog with HD short of surgery are - enough exercise to keep muscles strong in the back end; anti-arthritic supplements such as Cosequin. Talk to your vet, but that means so far as I know not exercise like throwing a ball and having the dog accelerate and decelerate to and from a hard run, but steady motion like long walks. There are supplements that help a lot of dogs. I had one of my Rottweilers on Cosequin and gave her Adequan shots sub-q every 2 weeks. She had moderate HD.