My little one did the same thing when he was first getting used to the concept of 'winter'. If it was too cold, he just wouldn't want to walk. If we were in the middle of a walk, and he started to get cold, he would just drop where he was and refuse to budge. But, a warm fleece jacket on him will keep him running outside for hours! He is a very skinny beagle, standing about an inch taller than his big sister, but 5 lbs lighter. We are trying to fatten him up but every time we give him more food he just goes and gets taller!