From AKC canine myth busters.
Myth: I have to shave my dog’s coat because he looks so hot.
Fact: Many double-coated breeds have weatherproof coats that not only keep them warm in the winter, but also serve as insulators in the summer. A dog’s coat protects him from heat, sunburn, and even skin cancer. Shaving removes their protective layer, putting the dog’s skin at the mercy of the elements. Think of a heavy coat as your dog’s sun umbrella. Also, because dogs don’t sweat the way humans do, shaving the hair coat doesn’t actually help facilitate the thermoregulating process. Keeping a double coat in good condition with regular brushing is the best way to help a dog stay cool in summer.