General Thermoregulation of Dogs
Used with permission from  Allsorts' Dog Pictures

Dogs maintain normal body temperatures around 101.5⁰F.  Smaller dogs may maintain slightly higher temperatures while larger dogs may maintain slightly lower temperatures (Johnson 1977).  The following are methods dogs use to maintain steady body temperatures:

Panting

• A dog's primary method of cooling is evaporative cooling from the respiratory tract through panting.  When a dog pants it provides increased air flow over moist surfaces in the upper respiratory tract through rapid, shallow breathing.  The increase in air flow causes an increase in evaporation from the upper respiratory tract.  Increased ventilation associated with panting can lead to alkalosis, but this can be counteracted by a shift to shallow respiration at increased frequency.  The increased ventilation will then be restricted to the upper respiratory tract.  Panting also requires muscular work which produces heat, but dogs use the elastic properties of the respiratory tract to minimize such heat production.  Due to its elasticity a dog's respiratory tract has a natural frequency at which it oscillates with little muscular work.  At the onset of panting respiration rate increases rather suddenly from around 30-40 respirations per minute to around 300-400 respirations per minute.  Under a moderate heat load a dog alternates between brief periods of panting at high frequencies and periods of normal slow respiration (Schmidt-Nielson 1997).

Skin and Fur

• A dog's skin is made up of the epidermis and the dermis.  The epidermis is an outer layer of cells that constantly gets replaced.  The dermis is found under the epidermis and supplies it with nerves and blood.  Sweat glands are found in the dermis along with sebaceous glands which feed oil into hair follicles in the epidermis to lubricate the skin.  Hair grows up through follicles from papillae in the lower epidermis.  More than one hair grows through the same follicle in dogs and one hair from each follicle, the guard hair, is usually longer than the others.  Dogs can achieve piloerection, raising of the guard hairs, by contracting or lengthening muscle fibers in the dermis (Whitehead et al. 1999).  A dog's fur insulates it against cold and heat (Johnson 1977) with the degree of insulation increasing with fur thickness (Schmidt-Nielson 1997).  Dogs normally shed twice a year, in the spring and in the autumn.  Shedding in the spring gets rid of hair that is not needed for the summer and shedding in the autumn is in preparation for growing a thicker coat for the winter.  Dogs who live indoors may shed for longer periods of time than those who are kept outdoors because conditions such as artificial lighting and central heating interfere with the fur's growth cycle (Whitehead et al. 1999).

Sweating

• Although dogs have sweat glands, located primarily in the pads of their feet and in their ear canals, sweating plays a minimal role in their thermoregulation (Whitehead 1999).

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