The metabolism of the dog is really best adapted to cold climates, as they do not possess very efficient heat-regulating mechanisms. Humans lose heat mainly through the cooling effect of the evaporation of moisture from the surface of the skin. The moisture is supplied by multiple sweat glands.
Dogs do not possess sweat glands and rely on the evaporative effect of air drawn over the moist surface of the tongue, which can be vastly expanded to expose its blood vessels to the maximum surface area. The dog increases the evaporative effect by drawing in and expelling air over the tongue as quickly as possible. The hotter the conditions the larger and brighter pink the tongue appears, the more the dog salivates and the harder it pants.
In very hot conditions and where the dog has no ready access to water, eventually, it can no longer produce adequate amounts of saliva and the surface of the tongue dries out. It is at this point that its temperature begins to rise and if some relief is not available the dog begins to suffer heatstroke.
Various factors contribute to the likelihood of heatstroke. Dogs exercised in extreme conditions without water, of course, are at the most risk. Dogs shut in cars or confined spaces without adequate ventilation are in danger. Some hyperexcitable dogs or very young puppies that become frightened during car journeys can increase their body temperature by overactivity.
Breeds with very heavy coats, dark-colored dogs or overweight animals suffer more in the heat. Older dogs with failing hearts find the summer far more trying than the colder months.
On very hot days, avoid exercising the dog during the hottest part of the day unless it has access to the lake or river. It is important to maintain regular exercise but try to arrange it for the early morning or night. Do not feed the dog just before exercise, and preferably in the coolest part of the day.
Consider clipping the long-haired dog for summer. Not only will it be much more lively but it is easier to find grass seeds and ticks, easier to dry after swimming and is less likely to be worried by fleas.
If your dog will not settle in the car or becomes carsick, ask your veterinarian for some tablets which will calm the dog and prevent vomiting. Care should be taken with such tablets before traveling by air because the effect of any tranquilizer seems to be magnified during flying.
If you have to leave the dog in a stationary car, make sure that there is a good ventilation and that the car is totally shaded. Return frequently to check the dog, as the changing position of the sun can mean it streams through one window, making the interior like an oven. When traveling, take the dog’s bowl and plenty of water and give it frequent opportunities to lap.
The signs of heatstroke in the dog are quite obvious. The dog becomes very distressed, its respiration becomes very fast and shallow and the tongue, although vastly expanded, is usually dry and bluish. Get the dog into the coolest available place as quickly as possible. A tiled bathroom or concrete floor is preferable to carpet.
If outside, find the shadiest place, preferably with a breeze. Wet the dog completely with cold water and sponge cool water over its tongue. As the body temperature falls, its breathing will become more regular, with deeper, more productive respirations. The tongue will change from blue to a more healthy pink and the dog will become more aware of its surroundings. Keep the dog as quiet as possible and concentrate on giving it fluids rather than the solid food.