Background

Heat loss in dogs is primarily via convection, conduction, and evaporative loss, contrasted to radiant heat loss of humans.1 Panting is the only significant cooling mechanism for dogs; they do not have widespread sweat glands. Normal MWD rectal temperatures are 99-102.5°F (37.2-39.2°C), and it is common for rectal temperatures to be > 106°F (41.1°C) during exercise with no adverse effects.2,3 However, each MWD’s heat tolerance is different, and fatal heat stroke cases have been associated with rectal temperatures as low as 105.8°F (41°C).3,4,5 A study in exercising MWDs demonstrated that body core temperatures up to 106°F (41.1°C) are common in healthy MWDs during work, and that core temperature continues to increase over the course of 15 minutes after exercise.3 During recovery, dogs not affected with heat injury rapidly normalized their temperatures within 15-20 minutes.

Heat-induced injury in MWDs usually develops secondary to heavy physical exertion in hot and humid environments. MWDs may also develop heat-induced injury if left in or trapped in closed vehicles or containers or due to partial airway obstruction of any cause. Risk factors for MWD heat injury include inadequate acclimatization to high-intensity activity and climatic conditions, inadequate hydration, a history of prior heat injury events, and obesity.5-8

There are three types of heat-induced injury in veterinary patients, based on the severity of the resulting injury: mild (“heat stress”), moderate (“heat exhaustion”), or severe (“heat stroke”). Severe heat injury in dogs is associated with a mortality rate of 50-64%.4,6,9,10 Heat injury in dogs can progress very quickly. Rapid treatment as soon as the first clinical signs are noted is imperative.