Poor pup, I hope it isn't anything serious.
I will say that when Cesar was 5 months (only had him for 2 months at this time) and I'd walk him the poor dude would tucker out and need to be carried. He wouldn't limp though and when he got home he would just pass out.
Now that he's older, he runs with me everyday (not in the winter obviously) for about 1.5-2 miles. And yes, he runs the entire time like a mosh dog. He never seems to run out of energy and seems to enjoy the jog, and sometimes we'll even go for another 30 minute walk in the later half of the day and he never has any problems, so I will say to you that I doubt it's the distance that the dog is walking that is causing the problem (but ur pup is much younger).
I would keep him inside and not play any games that require him to run, and not take him for any walks for a week or so and then take him for a walk to see if maybe he's just got a hurt leg and you're not aggravating it with exercise. |