Dehydration and Thermoregulation in Dogs
	Photographed by Robin and Harold Winter. Used with permission from Narnia Kennels.

• 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 1984).

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