by Janice Willard DVM, from the June 2006 Newsletter

On the country road near my house, I recently watched a jogger run by, with springing step and body glistening with sweat. Behind him, doggedly trying to keep up, trotted his dog, its tongue hanging out so far it seemed he would trip on it. While many would smile at the sight of these two, I’ll admit that I felt concern for the danger into which this person was unknowingly placing his companion.

One of the things we have in common with dogs is that we both evolved for endurance activities. However, there is an important difference: humans are adapted to dissipate heat, while dogs are not. 

“Dogs are good at retaining heat,” says Ray Coppinger, Ph.D, biologist and author of one of my favorite books, Dogs, A Startling New Understanding of Canine Origin, Behavior and Evolution, “but they are lousy at dissipating heat.” 

Humans and dogs both evaporate water to cool their bodies. But humans use the entire surface of their body, while dogs only sweat from the pads of their feet and use the evaporative surface of their tongue. Dogs increase their breathing rate to pull air over that evaporative surface (panting) but this requires energy, which then generates heat, and is dependant on a properly functioning respiratory system to work.

Dogs have richly vascularized muscles that are highly metabolic. This gives them significant athleticism, but also generates large amounts of heat. And a metabolic process for cooling that we both share is that when we are getting hot, the body floods blood vessels near the skin to aide in cooling—but while our skin is mostly bare, dogs are covered with fur. Not many of us would exercise in a fur coat in the summertime. 

We usually will quit when we are getting overheated, but so caught up in enjoyment of what they are doing, a dog might not. So while trotting behind a jogging owner or chasing a ball in a park, a dog’s body temperature can become so elevated, that it is in serious trouble before the dog can recognize it and stop. Put simply, on a hot day, a dog can literally run itself to death. Also being left in a car, even with the windows open in the summer, or tied in direct sunlight can quickly create dangerous, even fatal conditions for a dog. Humid conditions increase the danger.

If your dog has become overheated, here are some things to know:

An overheated dog might be prostrate and panting, unsteady on its feet or actually lapse into unconsciousness. Lack of panting may occur if the dog is going into shock. The dog might vomit or have diarrhea and the mental status can vary from alert and anxious, to depression, stupor, unconsciousness, and even seizures.

A case of ‘heat stress’ in a dog may resolve on its own, once conditions for cooling itself are provided. But a moderate to severe case, called ‘heatstroke’ will need the services of an emergency veterinarian as this is a very serious condition, potentially causing death, and expensive to treat.

If you suspect hyperthermia or heat stroke in your dog, call an emergency veterinarian immediately. If able, take a rectal temperature as it will give valuable information for the veterinarian. Cool the animal by gentle hosing with tepid water or immersing for a short time (no more than 15 minutes) in cool or tepid water (don’t let their head get in the water). Wet their fur and blow air over them with a fan.  

Be careful of overcooling your pet—once they have overheated, the thermoregulatory centers in their brain are impaired and it is possible to overshoot and get them too cold—both conditions, overheating and under-heating can cause shock and multiple organ failure.

Prevention, therefore, is the most important thing that you can do. Pay attention and don’t let your dog get overheated to begin with. Recognize when conditions are too hot to exercise your dog and if out with your dog, stop and let him cool down before he starts to pant heavily. Summertime can be the most fun time to enjoy with your dog, just remember, as a rule, keep your dog cool!

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