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 has well and truly arrived with its thunderstorms and high temperatures. I have discussed noise phobias in my January 2009 column. In this column I would like to talk about heat stroke in dogs.

Heat stroke occurs when the dog’s heat dissipating mechanisms cannot adequately cope with heat production, such as during severe exercise, or are impaired. More than 70% of heat loss occurs from the body surface by radiation and convection and as the environmental temperature increases to near body temperature, this obviously becomes less effective as there is no differential.

Evaporation then becomes the most important method of cooling. Evaporation takes place from the fine curled bony structures (turbinates) in the nose and also from the tongue and mouth. You may notice that when your dog is hot his tongue hangs out and appears much wider than usual. This, as well as increased salivation, is to promote evaporation.

Dogs don’t sweat through their skin, but only from the skin of their paws, which severely hampers their ability to lose heat. Increasing humidity decreases the efficacy of evaporation as a heat loss mechanism. Certain factors may predispose a dog to developing heat stroke. Obesity increases insulation and thus decreases heat loss through the skin. Excessive exercise in a hot and humid environment, even for a short period, can initiate heat stroke. This is especially important with working dogs, and also dogs which play vigorously with the children, for example around the swimming pool. It’s okay if they are also swimming.

Brachycephalic (flat nosed) breeds such as boxers, Staffordshire terriers and bulldogs are predisposed to developing heat stroke because the surface area of their nasal turbinates is decreased, resulting in less evaporation. Many of them, especially the bulldog, are also inclined to develop swelling of the structures in the throat as they pant, which further complicates the situation by decreasing air movement and thus evaporation and may also cause them to die of suffocation.

Prevention is better than cure and it is important not to allow your dogs to exercise, even for a short time, in the heat of the day. Luckily, on the highveld, humidity is not a big problem. If you notice that your dog is panting and appears distressed, you can try to cool him down.

Ice packs, wrapped in paper, can be placed under the front legs in the “armpit”, in the groin and over the jugular (neck) veins. The rest of the dog can be drenched to the skin with cool water and placed in front of a fan, on a cool tiled floor.

It is important not to put ice packs onto other areas as the cold will cause the blood vessels in the skin to constrict and thus decrease the amount of heated blood reaching the skin for evaporation. The larger blood vessels are too big to constrict. If this doesn’t control your dog’s distress in five to ten minutes, you need to get him to a vet. Heat stroke causes damage to the lining of all the blood vessels in the body and starts a cascade of changes which could be fatal.

Never leave your dogs in a car parked in the sun or part sun, even if the windows are turned down a little, as the temperature rises too much in such a closed environment.