In this column veterinarian Dr Liesel van der Merwe provides practical assistance for common problems in companion animals. She is a specialist physician at the Onderstepoort animal teaching hospital and a senior lecturer in the section of small animal medicine. Send your questions to This e-mail address is being protected from spambots. You need JavaScript enabled to view it

Dr Liesel van der Merwe

Summer is here and it is nice and hot; perfect weather for playing outside, swimming and generally being out and about. Many of us love including our pets in these activities, but be careful; this is also when your dog can get heat stroke.

Heat stroke occurs when the animal is unable to lose normal body heat which is produced by the normal physiological functions of the body. Normal temperature in dogs is 37.5 – 38.5°C. A temperature of 42.5°C is life threatening as all the enzymes and proteins in the body start becoming damaged and nonfunctional.

Humans and horses keep their body temperature low by perspiring. Evaporation of this fluid also cools the body. Dogs do not have sweat glands in their skin and have only a few in their foot pads and are thus limited in their ability to lose heat. Normal heat dissipating mechanisms in dogs include radiation and convection from body surfaces, which account for 70% of heat loss, and panting. Panting becomes increasingly important as the environmental temperature rises to nearer body temperature, thus decreasing the efficacy of loss through the skin.

The tongue muscle relaxes to increase its surface area and the air movement promotes evaporation. Increased salivation also promotes evaporation which is cooling. As air moves through the nasal passages it cools the blood present in the nasal turbinates, thin curled bones lined with a moist membrane, and provides a large surface for the humidification of air in normal circumstances.

As the humidity increases the dog’s ability to cool off through evaporation through the nose and mouth is compromised.

Heat stroke will develop in normal dogs exposed to severe temperatures or in dogs with poor heat dissipating mechanisms, such as fat dogs and brachycephalic breeds (flat-nosed dogs) in more normal environmental conditions. Risk factors are obesity, a thick fur coat which acts as an insulator, brachycephalic breeds, such as boxers and bulldogs, and overactive dogs.

Environmental factors are hot humid weather conditions, the animal being placed into a relatively closed area in hot weather, such as the car, a kennel or small courtyard, a lot of activity during the hot periods of the day, and excessive playful exercise.

Even on a cool day, the inside of a car can heat up very rapidly. Never leave your dog in a car in the sun. Also limit heavy exercise in the middle of the day and always ensure that sufficient water is available.

Heat stroke symptoms include vigorous panting which doesn’t subside once steps are taken to cool the dog, dark red gums, lying down and not wanting to stand, thick saliva, disorientation, collapse and loss of consciousness.

Immediate action and early veterinary intervention in severe cases positively affect the outcome. Move the dog into a shady and cool, breezy area. Drench the dog with cold, not ice water. Ensure he is wet through to the skin. Start a fan if you can to maximise evaporation.

If you have icepacks, wrap them in paper and place them over the major blood vessels in the groin, under the front legs in the armpit and against the jugular veins in the neck. Ice water is not recommended as it will cause the small blood vessels in the skin to constrict and will actually decrease heat loss. The large blood vessels will not constrict in response to the cold.

You should expect a reasonably rapid response (within five minutes) to this treatment. If not, immediately seek veterinary attention. Wrap your dog in a sheet and continue wetting the sheet on the trip to the vet.

Heat stroke is dangerous because the high temperatures damage the lining cells of all the blood vessels in the body. This causes severe inflammation and a predisposition to clotting, resulting in organ failure. Your veterinarian will immediately place the dog on an intravenous drip as the circulatory system collapses in many cases.

Brachycephalic dogs may need to be anaesthetised as the panting causes the structures in their throat to swell, further hampering heat loss and also causing suffocation. Once they are anaesthetised, a tracheal tube or tracheostomy tube is placed to facilitate breathing, and drugs to decrease swelling are administered. Severely affected dogs have a high mortality and die of lung and kidney failure as well as over-activation of the clotting system called DIC.

Prevention is certainly better than cure.