How do canine athletes regulate body temperature?

The canine athlete regulates its body temperature somewhat differently than its human or equine counterpart. The human and horse utilize sweating capabilities. The dog has minimal sweating abilities. The only site on the dog’s body that has anything similar to sweat glands is located around the pads of the paw. The dog must use other mechanisms to manage its body temperature. This is why a lot of the training techniques used by the human and equine athletes are not applicable to the canine athlete. An important consideration is that the normal body can acclimate itself to many of the conditions that can induce an increase in body temperature. A proper training and conditioning program combined with the correct nutritional plan can help to minimize most increases in body temperature that are related to exercise.

Temperature Regulation

The average body temperature of the dog is 101.5°. The normal range is between 100° - 102°. These are core temperature values and are based upon rectal thermometer readings. Temperatures can vary throughout the body, but the core temperature is used by the body to maintain homeostatic conditions. Because of this, the body temperature can be used to assess the physiological status of the body.

Exogenous vs. Endogenous Pyrogen 

The body’s temperature can be affected by exogenous factors or endogenous factors. A fever caused by a bacterial infection is an example of an exogenous pyrogen. In this case the bacterial has entered from outside of the body to create the increase in temperature. A fever caused by a tumor or internal inflammation is an example of an endogenous pyrogen, where the fever is caused by an internal stimulus. This article will focus on the metabolic conditions surrounding physical activity that can cause an increase in core body temperature. How dogs cool down their body temperature  The temperature control center, or thermostat, is located in the hypothalamus area of the brain. It regulates the body’s temperature based on information from temperature recognition sites located in the skin and throughout the body. These cold and hot receptors send signals to the thermostat, which initiates the mechanisms that are used to maintain the body’s temperature at a functional level (Figure 1). The most recognized mechanism used by the dog to cool down is panting. The surface of the respiratory tract is wet and the evaporation that occurs as the air passes over the surface acts to enhance heat loss. Another metabolic mechanism used to create heat loss is altering the body’s blood flow. In heat extremes, the body will divert blood towards the surface and away from internal components. Heat is dissipated from the blood flowing at the body’s skin surface. To further help with this dissipation, the dog will change its posture to enhance the surface exposure. A dog will extend its legs to increase the surface exposure when it is hot and curl up when it is cold. Another heat reducing mechanism is the brain’s logical thought process. When a dog determines that it is hot it will seek out cooler locations (i.e. shade or water). It will decrease its workload and efforts. It may start laying down or sitting during the activity. It has recognized that it is hot and continuing these activities will make it hotter. The normal dog will use these mechanisms to help from overheating.

Temperature Regulation Disorders

Diagnostically, it is important to determine the cause of increased body temperature. The treatment choice will be determined by what causes the problem.

Elevated Body Temperatures

Increases in body temperature can have many causes. These causes can be environmental conditions or internal elements. Outside temperature and relative humidity are two examples of environmental causes. An elevated outdoor temperature (90° or higher) can be enough to increase the metabolic temperature. Humidity can be a factor. The dog uses respiratory surface evaporation as a means of heat dissipation and if the humidity is too high, it will reduce the evaporative capabilities. During exercise muscle activity is the main internal heat producer. Of the energy expended by the muscles, 20% - 30% is utilized for work and 70% - 80% is released as heat. This heat acts to increase the body temperature during exercise. An increase in body temperature as a result of work is a normal event that is not detrimental to the conditioned dog.

Hyperthermia versus Heatstroke

Hyperthermia is defined as a temperature higher than normal. If a dog’s normal range is between 100° and 102°, then any temperature recorded higher than that would be considered hyperthermic. Most athletic or working dogs will have an increase in body temperature to a level that would be hyperthermic. More often than not this increased temperature does not create a medical emergency. Heatstroke is a metabolic event that leads to a medical emergency. Clinical signs of heatstroke include rapid breathing and collapse. It is very common to have vomiting and diarrhea. Disseminated intravascular coagulation and cerebral edema can also occur. The oral mucosa may appear bright red and the core body temperature can be 109° or more. Heatstroke occurs when the dog’s body cannot handle or manage the increased metabolic temperature. It is important to distinguish the difference in these two conditions. A body temperature that causes heatstroke in one dog may not cause any problems in another dog. Also, a dog acclimated to working at a higher body temperature won’t be as susceptible to heatstroke as a dog that is not conditioned to this working situation. It is very common to see temperatures from 102° up to 107° in dogs that are not exhibiting any signs that would be typically seen in dogs suffering from heatstroke. An increase in body temperature during activity has been reported in Racing Greyhounds, Trial Labrador Retrievers, Hunting English Pointers, and Hunting Foxhounds (Figure 2). The dog’s body adapts itself to its activity level. Clinically, the normal resting body temperatures for these dogs can be 99° - 100°. This lower homeostatic body temperature is a result of the body acclimating itself to its routine activity. This information requires us to readdress how we use normal core temperature values as a diagnostic tool when working with the athletic dog. When a dog suffers a heatstroke event during a working session we commonly evaluate the dog’s body temperature. Many times it will be 102° or higher. Because normal working temperatures range from 100° – 108°, this means that the dog’s thermoregulatory system is impaired. The first action is to treat the dog, but once the event is over we should determine where the system broke down. It might be possible to fix the problem through a change in our conditioning and nutritional programs.

Summary- Take away!

In this article we have discussed the thermoregulatory system and its role in the athletic and working dog.

1. It is important to note that working temperatures of 102° - 108° are normal during times of activity or performance. Temperatures of this level are not life threatening to healthy, conditioned dogs.
2. A normal athletic dog will recognize when it is getting too hot and will alter its activity accordingly.
3. The handler can use these alterations to alert them that it is time to end the workout session.
4. If the dog is not able to handle the tasks that are required for performance, then the training, conditioning, and nutritional program of this dog should be reconsidered.
5. Heatstroke is an event that occurs as a result of a breakdown of the thermoregulatory system.
6. It is important to determine the cause of this breakdown so that we can determine the method of repair or treatment.