I've been waking up at 6 am to run and I bring Gandalf along. Before we go I wet his head , inner legs, and paws down to try to keep him cool. We only go a couple miles on soft dirt and grass in a very shady park. It's starting to get hot out but at 6 am I find it pretty comfortable, we even have a halfway point water break on our runs. G seems to be struggling to make it even a mile, he just tires out and lags behind to the point I have to stop and walk. I'd hate to have to leave him at home... kind of the reason I got a GSD , I wanted a good athletic partner. My old GSD (dark sable) used to run with me 10-20 miles per day in conditions much worse than this. G has been doing well, good poops, just got a health check up and the vet said he looked great. Good weight too. What's the deal..? Im not a particularly fast person and I would expect your average gsd to be able to out pace a human. We've done rollerblading in the past and he handled that pretty well, but it wasn't so hot out. I feel like it must be the weather bothering him. Any tips on keeping him cooler?