Hydrated dogs can tolerate exposure to high ambient temperatures for
extended periods of time. Dehydration leads to elevated body temperatures
in heat-stressed dogs.
Dehydrated dogs under heat-stress have higher rectal temperatures and
lower respiratory rates, evaporative water loss, cardiac output, and carotid
blood flow than do hydrated dogs. Rectal temperature increases with
increasing ambient temperature in both hydrated and dehydrated dogs, but
dehydrated dogs' rectal temperatures are higher than those of hydrated
dogs. Frequency of breathing and evaporative heat loss also increase
in both hydrated and dehydrated dogs under heat stress, but dehydrated
dogs have lower frequencies of breathing and evaporative heat loss rates
than hydrated dogs. The reduction of evaporation rate seems to be
accomplished mostly by decreasing respiration rate. The decreased
cardiac output observed in dehydrated dogs exposed to heat is probably
due to reduced blood flow to several vascular beds, not all of which are
involved in thermoregulation. The rate of blood flow through the
carotid artery increases with evaporation from the upper respiratory tract
in hydrated dogs.
The effects of dehydration on thermoregulation in dogs exposed to heat
may be mediated by increased osmolality of body fluids and reduced plasma
volume. Dehydration can cause these changes in body fluids.
Dogs may also behaviorally thermoregulate as a response to dehydration.
In one study hydrated dogs could be observed making constant adjustments
in posture and shifting the position of the head and limbs. They
were also alert to their surroundings and held their heads up. Dehydrated
dogs in the experiment made few movements of the heads and limbs, generally
laying with the head resting on the forelegs (Baker
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