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
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 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. |