[yorkietalkjilly]

Maybe prolonged walking is getting hard for him for some reason or he's afraid or dreads a portion of the walk, as he knows after a certain time he will start to hurt. I'd check his paws, toenails for a start for any problems there. Plus, any time a dog changes its behavior, you know that it's time to see the vet and have him checked out for possible medical problems, complete with blood work, fecal check and Ua.

If he clears that medical work-up, it's likely he's dreading a dog or scent or something he's worried about on the route you walk. Try taking him to a different area a few blocks away for his walk and see if after a time or two there he won't start to check it out and explore. If not, he could fear that he will run into what he dreads even on that walk and it could take some time but at least early on if he doesn't act interested at all, you know you've got a problem with the outside situation, an issue that will need some time to track down.

I'd change out his collar and leash just in case he's having a problem with any part of that apparatus. Sometimes walk aversion is as simple as the harness is rubbing him in a place he doesn't like or his collar is too tight, the leash reflect light or squeaks or makes a noise and makes him anxious. Take him out a different door if possible. Change up his routine in ways like that.

Has he ever been fearful or anxious of things before or had any kind of panic attacks? If so, you might consider trying a Thundershirt on him or even giving him a mild sedative for a day or two as you start to rehab him. Plus, you will need to remain calm and upbeat, not anxious or worried about him and his concerns. He'll look to you for guidance if he's anxious so try to keep on staying positive and forge ahead and taking along a ball/squeaky toy or something to toss ahead and see if you can't get him excited to chase it. Or, toss a piece of juicy boiled chicken ahead and see if he will walk ahead to it and so on until he's walked ahead for a while. Try various things like that. Clap your hands and act very excited and so forth while you are tossing the things to see if you can get him all amped up to play the game with the tossed object and go for it.

Watch his body language closely while he's out and about and see if his ears are going up or back or out to the sides or he's looking about nervously or acting shy or shaking, things like that. Likely, if he's not hurting or ill, something - even some odd sounds or noise or scent - has spooked him and over time and working with him with toys and treats and new areas, he might start to come around and accept that his walk is not bad after all.