Heat Stroke – Understanding Causes

The following reprint of an article first published in Dogs in Canada in 2004 offers excellent background on the causes of heatstroke in dogs in all kinds of weather. Dogs are very sensitive to temperature and need careful monitoring when under heat stress or in conditions that can compromise their ability to regulate their body temperature.

Hot Dogs: Warm weather is not the only cause of heat stroke

Reprinted from Dogs in Canada, March 2004 Issue

I thought I knew pretty much everything about how to prevent heat stroke in dogs. But a recent experience sent me to the library to learn more about how dogs regulate their body temperature.

I was at a dog show in a fairground’s farm building, chatting with a friend outside the obedience ring, when I hard a snorting noise approaching. I turned and saw a tall, athletic-looking young man with a matched pair of Bulldogs – a clear exception to the owners-look-like-their-dogs rule.

The noise wasn’t caused by the man blowing his nose, but by his dogs struggling to breathe as they walked. As I stepped outside, I noticed what a beautiful day it was for early fall in the mid-Atlantic – temperature about 68 degrees fahrenheit and very low humidity.

The next day at work I was asked by a colleague to look at a dog that had died at the show and been brought in for a post-mortem examination. I was shocked to see that it was one of the Bulldogs. The owner reported that he had left the dog in a wire crate in his minivan, in the shade, with the van’s back door up and all four side doors wide open. Even more amazing was the fact that the dog’s tongue was twice as long as the dog’s head from muzzle to the back of its skull. No wonder the dog was unable to pass enough air through its mouth and throat to cool itself.

Canine cooling

We all know that dogs have a lot more trouble with extreme heat than with extreme cold. As the ambient temperature rises, our canine companions initiate an escalating set of cooling mechanisms, including reducing activity, panting, stretching out on cool surfaces, sweating through the footpads, and hanging the tongue out of the mouth. When training your canine in warm weather, watch your dog’ tongue. When it gets wider at the tip (the dog uses the muscles in the tongue to enlarge the tongue to further increase evaporative surface area), that is the signal that your dog has just used his last cooling mechanism – it’s time to take a rest and get him to a cool area.

Brachycephalic dogs – those with flattened faces, like Pugs, Pekinese and Bulldogs – frequently have excess tissue in the mouth and throat, which prevents efficient passage of air. These dogs are exceedingly susceptible to heatstroke, and training outdoors in warm weather should be avoided.

One cooling mechanism that many people aren’t aware of is that dogs dilate the blood vessels in the skin to exchange the warmth of the blood with the cooler surface skin. That’s why short-coated dogs and dogs with single coats frequently suffer more in the heat – they don’t have the layer of insulating coat between the skin and air that double-coated dogs have. It is important that double-coated dogs not be shaved in the summer; although occasional bathing and frequent grooming will help remove dead hairs and thin out the coat, allowing more heat exchange.

Warm weather is not the only cause of heatstroke. Muscular activity can be dangerous as well, especially when combined with warm weather. This can be a particular problem for the canine athlete. Even when a dog is sleeping, 25 per cent of its body is provided by the muscles. But when that dog uses the muscles to exercise, the amount of heat produced by the muscles can increased by 60 times! Working dogs’ body temperatures may rise from normal (approximately 100 degrees fahrenheit) to 105F or even higher. That’s why long-distance mushing dogs become overheated at ambient temperatures as low as 0 degrees fahrenheit.

Warming ways

The same double coat that can provide insulation from the heat also insulates dogs from extremes of cold. The air trapped in a dog’s coat acts like the air in the fibreglass insulation in your walls. If the dog’s coat gets wet, however, the insulating value of the coat is rapidly lost. Add wind to the formula and a dog’s internal body temperature can drop rapidly. Dogs curl up in cold weather to reduce the amount of surface area over which cooling can occur.

The fact that dogs sweat through their feet can become a problem in cold weather. If the dog exercises and the pads begin to sweat, the warm sweat may freeze snow to the feet, forming ice balls that stick to the hair between the toes. These cause discomfort and can even cut the pads if the dog continues to exercise in spite of the ice balls. By trying to chew the ice balls off, the dogs just adds to the problem by adding saliva to the mix, which then attracts more snow, forming more ice. This is a major reason why many mushers’ dogs wear booties.

Fact: Small dogs are much more susceptible to extremes of both heat and cold. This is because they have more surface area relative to their body mass. In the summer, they have relatively more skin to absorb the heat, and in the winter they have relatively more skin to lose the heat.

Fact: One of the best ways to help your canine teammate recover from exercise and overheating is to provide antioxident supplements. Depending on their body weight, canine athletes should be supplemented with 250 to 1,000 milligrams of vitamin C and 100 to 400 IU of vitamin E per day.

Fact: When people and horses cool themselves by sweating, they lose both fluids and electrolytes – ions such as chloride and sodium. But when dogs pant, they lose water vapour only. That’s why it’s important provide cool, fresh water, not electrolytes, to replenish what your dog has lost. If you give electrolytes, you dog might actually become more dehydrated, because the excess electrolytes in the gastrointestinal tract can draw water from the body into the intestine.

Author info: Chris Zink, D.V.M., Ph.d., award-winning author of Peak Performance: Coaching the Canine Athlete, has put over 50 obedience, agility, retrieving and conformation titles on dogs from three different groups. Contact her at www.caninesports.com.