Trying to Get Swole (Again) with my Dog for the Deaf

First off apologies if this is in the sidebar. I didn't see anything directly related to muscle training, only obedience training.

Long story short, I live with a Dog for the Deaf. We both used to be ridiculously musclebound. I got into drugs/eating disorder and his owner slowed down (mostly bc of the winter season) with taking him for walks and now we are both skinnyfat.

I know how to feed and train myself to get fit again, but unfortunately there aren't starting programs for dogs, at least that I can find. How do I train the dog (he isn't mine, I'm not the deaf one) to get fit again? I've been taking him with me every other day on a 5k training plan (right now we are doing the 80-90% walking with bursts of sprints or jogs) and he seems to have a blast. Whenever we get back I give him a ton of water and a snack - usually a teeth-cleaning "bone", peanut butter, or some of an unseasoned baked sweet potato.

What am I doing wrong, what am I doing right, what do I need to continue doing, what do I need to stop doing, and what do I need to start doing that I haven't been doing?

I BELIEVE he's a mixed breed but I'm not 100% sure on that. Here's a pic of him post-run (sunglasses for scale) in case his breed/size needs a specific workout routine.

http://m.imgur.com/9BDyYup

Edit: Milk and eggs are the holy grail for human bodybuilding and powerlifting. Can dogs eat those and if so how much should I be giving him?