Avoiding Heat Stress in your Greyhound26 June 2018
Summertime is a little closer and the recent warm sunny days have finally allowed us to believe we have emerged from the chill of winter and perhaps the wet start to spring may be behind us.
With warmer days on the horizon, it might be helpful to remind ourselves of perhaps the most avoidable seasonal catastrophe that might affect our dogs. This is of course heat stress and especially the increased risk when dogs are left in a hot car.
There are many ways we might approach prevention and the main thrust is the zero tolerance tolerance approach where the expectation is nobody should leave a dog in a car unattended. This works to an extent, especially at dog shows or other competitions but is not always practical and certainly lacks flexibility.
So what follows describes the physiology that leads to hyperthermia in hope that where the simple edict is not effective perhaps a more detailed explanation might help dog owners to avoid making a mistake that will haunt them for a long time. Believe me, killing your dog through ignorance or stupidity tends to play on your mind for a very long time.
Knowing why heat stress occurs may also help dog owners avoid placing their dogs at risk, for hyperthermia does not only occur in hot cars it may be a risk on a cold winter’s day or even during a walk in the park.
A little science
All mammals have physiology designed to keep body temperature within an acceptable range. In cool environments heat is conserved and in hot conditions heat loss mechanisms operate. This automatic regulation of body temperature is monitored and driven by areas of the brain.
Maintaining body temperature within a normal range allows metabolism and physiological functions to operate at an optimum rate. If body temperature exceeds these limits cellular survival is threatened, tissue damage may follow and death is a logical endpoint.
An efficient thermoregulatory mechanism is a characteristic of all mammals and dogs have a particularly well adapted system which relies on a rapid reduction of body temperature through panting. Panting is an automated process delivering rapid air movement across moist membranes in the mouth and nasal cavities. The resulting evaporation of watery saliva cools the blood in the underlying tissues and thus lowers the temperature of the body. The mouth and nasal passageways and the blood circulatory system are somewhat similar to the radiator and water circulation system used to cool the engine of a car.
Dogs have efficient salivary glands designed for the purpose of producing copious amounts of watery saliva and the blood vessels in the mouth and nasal passageways are numerous to ensure the cooling effect reduces the blood temperature efficiently. Circulation of the cooled blood reduces core body temperature.
Panting indicates a need to lose excess heat. In itself it does not indicate distress. It is an entirely normal physiological response and is broadly similar to the human who sweats in similar conditions. Consider a panting dog to be the equivalent of the sweating human. In humans the cooling process is via evaporation of sweat from the skin surface, cooling blood in underlying blood vessels in the deeper layers of the skin. This process is not functional in dogs because of the coat.
Canine body temperature is around 38.50C, thus summer weather in the UK rarely produces ambient temperatures that exceed body temperature. So generally cooler air is generally available to aid heat loss through pointing and respiration. Normal heat loss from the respiratory system usually moderates body temperature for much of the time on a warm day.
Three critical factors
Efficient heat loss in dogs relies upon three basic elements, evaporation of water, air movement and copious amounts of salivary secretion. If local conditions affect any of these three, heat stress is likely to occur.
For example, if the local environmental temperature rises above body temperature the normal cooling effect is compromised. Panting will increase evaporation from the mouth and tongue to increase cooling and thus a dog can survive conditions that are warmer than body temperature - for a short period.
Such conditions take place in enclosed spaces and cars are the obvious example but but a cage enclosed by a covering, a box or kennel with inadequate ventilation or a closed conservatory or greenhouse, are all capable of reaching very high ambient temperatures.
The confounding factors affecting the efficiency of panting all occur in confined spaces where ventilation is poor. Thus water evaporation become increasingly problematic as humidity rises and a panting dog will contribute to humidity in an enclosed space.
A reduced flow of saliva will occur where dehydration occurs reducing the amount of water for evaporation. This happens when body fluid levels deplete due to persistent panting and physiological countermeasures are triggered to conserve tissue fluid reducing the water available to produce saliva.
The final element is reduced airflow. As a dog’s panting becomes increasingly excessive, eventually the membranes swell in the mouth and throat, occluding airways which compromises airflow and a reduces the efficiency of panting. At this moment a dog is in a critical condition and body temperature will now rise rapidly as the cooling process is no longer effective.
The hot car
The temperature inside a car can exceed 400C in just a few minutes in direct summer sun with little or no ventilation. In practical terms a dog lying quietly and panting efficiently may be able to survive in these conditions for perhaps 10-30 minutes but as humidity rises or their supply of saliva runs out this will rapidly escalate to a serious problem. An agitated dog, stimulated by the adverse conditions, the absence of their owner or where strangers are stood close by, is likely to deteriorate much more rapidly.
Reducing the risk
Parking in shade and leaving windows open will improve the situation but does not remove the entire risk. Also, be aware some breeds are better at thermoregulation than others and so the type of dog plays a role here too.
Leaving a dog in a car has become stigmatised as unacceptable. Certainly leaving a dog in a car in direct sunlight, with inadequate ventilation or lacking water is reckless. Leaving a dog in a car, in the shade, with the rear tailgate and sunroof or windows open is defensible provided there is a regular check (at least hourly), free access to water and the dog is known to be generally tolerant of summer temperatures could be acceptable.
Not just a hot car
However, bear in mind that hyperthermia is not restricted to hot cars. During my professional career dogs have developed heat stress in private homes on hot humid evenings, at dog shows held on cold sunny days in spring and post-racing at greyhound tracks.
In each case there were situations that have contributed to the hyperthermia. It is personal opinion, but kept in a covered box or cage is one factor, extreme physical exertion or excitement is another or difficulty breathing associated with brachycephalic conformation is yet one more, but this is not a complete list.