Big dogs carry more fat reserves and have a greater heat storage ability than little dogs (surface to volume -ratio)Puppies for instance do not have the body mass to be able to survive rapid dehydration, and adult, or big, dogs tolerate better low temperatures.Small dogs have low body mass that make them lose heat easier. Even the long haired doggies can adjust their body heat as well as larger breeds.Dress your small dog when you take him outside on cold days. Small dog breeds are prone to chills because they have no winter undercoat to keep them warm. Clean the snow and ice from his feet when he comes in, especially if he is a long-hair breed. Ice balls can form on the hair in between his toes and can be quite painfulSmall dogs have smaller stomachs and small appetites. You will need to make sure your dog gets the proper nutrition in his small meals. Feed more often (3x per day) and provide high- calorie,with sufficient nutrition.Small dogs need more calories to maintain their body heat: they produce less heat than big dogs, and radiate more of their surface (skin).Watch out: small dogs tend to be more pampered and some of them are less active than big dogs. Therefor they can be overfed easily and hence; will gain too much weight.