Vizsladogs, Ltd.

Cooling Heat Distress

We try to share what people think about many topics. This is one such topic that many people have opinions about and anecdotes that seem to back up their views on what should be done. We have taken a snip of a Vizsla Listserv conversation (with the peoples permission of course) showing the various sides on this issue. If you would like to add something to this thread of conversation send us an email note with your opinions and view points. If it adds to the discussion we will add it to this article

If a Vizsla shows signs of heat related distress, or you are about to go out into a very hot field to work, should you douse the dog with water?

On Wed 15 May 1996 JP wrote I have watched too many field trialers dip dogs before a run. I'm not sure it can help the dog. Yet, if everybody does it, it must be right. So, for a doctoral comprehensive exam in exercise physiology , I asked the question whether a dog can acclimatize and what the best way to cool the dog would be...the doctoral student researched the topic for one week.

JP reported back on her query of the friend: "Just an opinion: Dogs do not regulate body temperature the same as would feel good to a hot human to pour water over them because they evaporate through the skin...dogs only evaporate through the tongue and the pads of the feet. It is really unknown whether dogs can evaporate if water is poured over their body. Evaporation depends on two factors, the ability to sweat a fine layer of fluid to be evaporated and the shunting of the primary blood flow (heat) to the skin so that heat can be lost. If the blood flow (which carries the heat) cannot shunt to the periphery or skin, evaporation will not lose that much heat from the dog. A dilemma exists when you put cold water over your dog before you run him...the water itself may stimulate a shunting of the blood flow to the core of the body where it will function to store even more heat...hence the dog becomes even hotter."

"Dogs also lose heat through convection...the transfer of heat from a warmer object to a colder object (the skin to the air, providing the air is cooler than the dog). Blood must be shunted to the skin for convection to theoretically, evaporation could work....but the water to be evaporated must hit the skin and not the dog's coat."

" Dogs can acclimatize, but not through the same mechanisms as humans...human increases plasma volume so that sweating occurs sooner and becomes greater...but human's primary cooling mechanism is evaporation. Dogs do not increase plasma volume or sweat better...they become more efficient in doing the work..hence producing less heat. For this habituation (not acclimatization) a dog must work in the environment they will perform in. Trained dogs have lower body temperatures than untrained dogs..doing the same amount of work."

"Fuel sources also contribute to the amount of heat developed during exercise. One study showed that dogs on a high carbohydrate diet had improved performance with lower body temperatures than dogs using more free fatty acids (fats). Bottom line is the three key thing for good performance in the heat...1) physical conditioning including exposure to the environmental heat loads...2) adequate water...3) adequate carbohydrate intake/stores."

Diane J. Blackwood (DB), whose credentials include a B.S. Zoology, Masters in Biomedical Engineering and current Ph.D. student in Wildlife & Fisheries Sciences, continued the discussion by stating: "I agree that dog's primary cooling is through panting and some sweating on the paws. I would say that for some dogs it does feel good to get wet on a hot day. Many dogs will gladly wade into water and some lay down in the water. This wets primarily the ventral surfaces. I know that studies have been done on horses that show that wetting the ventral surfaces helps to cool the horse better than wetting the whole horse. The explanation argued is just what JP said: Wetting the dorsal surfaces, and hence the larger muscle masses, tends to draw blood away from the surface, especially for cold water. Indeed wetting the dorsal surface with cold water can cause a horse to stop sweating, which can be dangerous if water cannot be reapplied and the horse continues to exercise (as on a long trail ride)."

"Most endurance racers (50 to 100 miles races) recommend using warm water (85-95 degrees F). They or their assistants deliberately draw water and let it sit in buckets until it is air temperature to have ready at check points or at the end of the ride. This way the water can be used on dorsal surfaces without causing the peripheral blood vessels to constrict and limit blood flow and hence heat exchange at the surface. Cool water and sometimes ice is used on the ventral surfaces where major vessels run closer to the skin. Granted, horses do sweat and cool by sweating naturally and hence have the vascularization to take advantage of this type of cooling. However, dogs can shunt blood from the periphery to deeper in the body or the reverse to help control body temperature through convection.

JP also wrote: "Dogs also lose heat through convection...the transfer of heat from a warmer object to a colder object (the skin to the air, providing the air is cooler than the dog). Blood must be shunted to the skin for convection to theoretically, evaporation could work....but the water to be evaporated must hit the skin and not the dog's coat."

DB responded that she assume that JP meant for evaporative cooling to work the water must hit the skin, not the coat. (water evaporates quite well regardless of the surface, hot pavement for example). "I disagree that the water must be on the skin to help cool the dog. Evaporation (as opposed to cooling through evaporation) depends on temperature and relative humidity. That is one reason a humid 95 degrees F feels so much hotter than a dry 95 degrees F. Any time one gram of water is evaporated it takes 539.55 calories. The specific heat of air is about 0.243 cal/g. So, the evaporation of one gram of water will cool 2220.37 grams of air by one degree C. Or, the equivalent of cooling 222.04 grams of air by 10 degrees C."

"This is how swamp coolers work. Water is allowed to evaporate off pipes that have air in them. The air is then circulated through the building with fans. Swamp coolers only work well in dry climates, since evaporation is faster in dry air (more grams/minute). Note: there is roughly one gram of air in a liter of air. Hair, among other things tends keep the same mass of air around an animal. It provides a layer of insulating air. This is how it keeps animals (and some plants) warm in cold weather. When water evaporates off hair, it will cool the air surrounding it. This is also the air in contact with the skin, hence enhancing convection cooling. Heat transfer due to convection heating is directly proportional to the difference in temperature. The greater the difference the faster the heat transfers, in this case from a hot dog to the cooler surrounding air. "

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