Most dog owners will be aware that high temperatures are dangerous for their dog, some of these dog owners will also know that high humidity levels pose a risk, but why exactly are they dangerous? Dogs use several different mechanisms to lose body heat, but high temperatures and humidity levels severely impact these cooling mechanisms. By being aware of the mechanisms dogs use to cool down, we can keep them safe, happy, and healthy year-round.
Cooling mechanism of dogs
Dogs use four main mechanisms to lose body heat, which are
Let’s have a closer look at each of the mechanisms.
We speak of heat loss through convection when the loss of heat happens through a fluid.
Fluids are substances that flow, like air and water. When air or water molecules flow across the skin, heat gets transferred. The rate of heat loss is dependent on the airflow, or flow of water, over the skin, and the difference in temperature between the skin and the surrounding air/water.
Heat loss through evaporation takes place through panting and sweating. Sweat is created by a sweat gland, and there are 2 main types of sweat glands seen in mammals, which are the eccrine glands and the apocrine glands. The eccrine glands main purpose is body temperature control, and to achieve this it secretes a fluid known as sweat. Humans have eccrine glands all over their body, and one of our main ways to lose body heat is through evaporation by sweating. Dogs however only have these eccrine glands in the paw pads, and their main sweat gland which is found all over their body is the apocrine gland. The apocrine glands main role is to release pheromones which helps them communicate with other dogs, and not to secrete a fluid that helps regulate their temperature, which makes that heat loss through sweating is minimal for them. The main way dogs lose heat through evaporation is by panting. By panting, the evaporation of fluid in the upper respiratory tract may account for 60% of their heat dissipation. As this form of heat loss uses a lot of water from the body, it’s important to hydrate well.
We speak about heat loss through radiation if the heat loss happens through the body or skin, but without the need of having movement or contact with another body or object. The heat loss just happens as is. When the body temperature of the dog rises, blood vessels in the skin will dilate, which results in an increase in blood flow. Blood gets directed towards the skin where excess body heat gets released into the environment. About 40% of a dog’s body surface heat loss happens through radiation alone. An important factor in heat loss through radiation is the size of the exposed skin surface.
We speak of heat loss through conduction when the heat loss finds place through physical contact with another body or object. A good example of this is when a dog lays down on a cold floor to cool down. To lose heat through conduction, cool objects will need to be available and hot objects will have the opposite effect.
The impact of the weather on these cooling mechanisms.
Without going into too much detail about how exactly the surrounding temperature affects each of the single mechanisms so as to not overcomplicate things, we can generally say that higher surrounding temperatures impact the effectiveness of most of these cooling mechanisms and they become less effective. According to Newton’s law of cooling (which applies to both heating and cooling), the rate at which an object cools down is proportional to the difference in temperature between the object surroundings and the object. What does this mean? A cup of hot water will cool down faster in a cold room than in a hot room. If we apply this to our dogs, this means that when the skin temperature of the dog is higher than that of the surrounding area, they will mainly lose heat to their surroundings. But once the temperature of the surrounding area becomes higher than that of the skin, most of these mechanisms (but not all) will actually result in them mainly gaining heat.
When temperatures are high, the main cooling mechanism is through evaporation. Anything that prevents adequate evaporation, like high humidity levels, will cause the body temperature to rise. This is exactly what makes high humidity levels in combination with high temperatures extremely dangerous, as all cooling mechanisms will be less effective. A decrease of effectiveness of heat loss through evaporation starts at humidity levels of greater than 35%, while humidity levels of around 80% will make panting ineffective.
When the cooling mechanisms of a dog can’t fully function due to high temperatures and/or humidity levels, their chance of heatstroke greatly increases. Being prepared saves lives, and recognizing heat stroke and providing first AID before going to the vet can increase the chances of survival from a range of 50% up to 80%. You can find our full heatstroke article here.
Living in the UAE, the weather conditions can be extremely dangerous for dogs. The high temperatures, and high humidity levels, will impact your dog’s ability to cool down and should never be underestimated. Heatstroke is deadly and can also happen after sunset.
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