I'm in the same boat as you are. My dog is 2 years old. He had surgery for his ED. Vet said he should be able to do most of the things he did before. I think swimming is the best exercise for them but like you I am waiting for it to warm up. I am going to play it by ear and see what my dog can handle and what makes things worse. He is very active and I would hate for him to not be able to do anything. Herding is one of the things we will try and also try him back in agility but at a easier rate than before. I did switch mine to a raw diet and that seems to help along with supplements. I think every dog is different and you will just have to see what your dog can handle. Good luck!
Rusti EAC, TN-N, TG-O, WV-N, NCC, NJC, CGC, GSD Diva
Jerry Lee AXP, MJP, OAC, TN-N, WV-N, NCC, NJC, SPJ, UAG1