Marcus Aurelius
Can horses handle the heat better than humans? The research says…
If you are a very fit person with low blood pressure, you may actually have a resting body temperature closer to 96, so there is a small range of differences in humans. The same is true of horses.
Normal body temperature for a horse is between 98 and 101. Horse temperature is normally taken rectally. When human temperature rises over 99 degrees and horse temperature rises over 102, it’s wise to take precautions. When your body becomes overheated you are in danger of hyperthermia (over heated). Hypothermia is when your body becomes too cool and can’t warm up. Both can lead to death if untreated.
So, who handles the heat better, horses or humans?
Well, a lot of that depends on external factors like humidity, wind speed, air temperature and whether there is shade and water available.
Both horses and humans cool themselves by sweating, which sets them apart from dogs, cats and birds which cool themselves through panting or respiration alone.
When horses and humans start to pant, it’s not a good sign. It basically means that they are no longer able to cool themselves by sweating.
When the combined air temperature and humidity levels exceed human body temperature (about 99 degrees) it becomes harder for humans to cool themselves by sweating. Sweat has to evaporate from the body in order to have a cooling effect. If the sweat sits on your skin, it actually traps heat in making you feel hotter, which is why some people say the heat in Savannah and other southeast coastal regions is worse than the heat in a place like Arizona or Utah, though once air temperatures rise above 90, most people agree, it’s HOT no matter what the humidity level!
Since a horse has a slightly higher body temperature than humans, they can handle slightly hotter air temperatures. A horse can still cool itself when the heat index is under 100, but once it rises to 101, they are on the same playing field as humans, so technically a horse can handle slightly higher temperatures, by 3 degrees tops, than humans.
This is about where the advantage ends though.
Both horses and humans who are acclimatized to the heat: i.e. have worked in the heat regularly for at least 14 days, will be better able to cope than someone who has not.
Also, the better physical condition you are in, the stronger your heart, lungs and muscles, the better able you can handle the heat.
Older humans and horses are often more at risk because they have slower metabolisms and may be less able to regulate internal temperatures and adapt to adverse environmental changes. They may also be on medications that can affect the body’s ability to adapt to heat stressors.
Older humans would be considered around 50 and up, and older horses about 10 and up, though again fitness and genetics can negate some of the effects of aging.
Humans actually have an advantage over horses when it comes to body size and the ratio of blood vessels located near the surface of the body.
When people get hot, they tend to flush red. This is because we have a huge web of tiny blood vessels leading to our skin. When we are hot, the blood is pushed outward to the skin where cool breezes, loose fitting clothes, sweating or cool compresses can help dissipate and wick away the heat from our bodies.
Horses have thicker skin, more ‘hair’, less skin surface to muscle mass and are less efficient at losing heat through the skin surface, which works out well in winter time, but puts them at a disadvantage in the summer.
Most horses will cool themselves naturally by laying down on cool damp soil or standing in the shade or near the water, something they can’t really do when they are being worked by humans.
So, as it stands, horses can handle the heat a little better than humans, but once they heat up, humans actually have the advantage and can cool down faster through natural means.
Let’s look further by comparing how much water each needs to replace the fluid lost.
Many people, especially when dealing with carriage horses being worked in the heat, will say that a carriage horse is not really working because he/she is just walking and to be honest, most of the research on humans and horses and heat stress has been done on working athletes, but veterinarians and human doctors estimate that a human will sweat out an estimated one liter of fluid per hour while moving normally in high heat and humidity compared to horse that will sweat out about 5 liters.
Heavy endurance athletes (humans) can sweat as much as 3 to 5 liters and heavy endurance horses can sweat out as much as 10 – 15 liters.
A liter is equal to about 34 ounces. A gallon is equal to about 3.8 liters.
So on average, a horse sweats five times more than a human doing the same amount of work. This also means that the average working horse is losing over a gallon of sweat per hour and horses can continue to sweat even if they are just standing in a hot area.
This brings up the question; is it better to sweat more or sweat less when it is hot out?
Sweating helps cool us off, but it also dehydrates us.
If you have ever gone for a long run or bike in the high heat and humidity, you probably licked the sweat dripping off your face and were surprised at how salty it tasted.
We don’t just sweat out water, we sweat out waters and minerals, often referred to as electrolytes, which are responsible for the transfer of electrical impulses across nerve endings.
If your electrolytes are not balanced (chloride, sodium, magnesium, calcium and potassium, primarily), you will have less efficient energy transfer and may begin to shake or feel weak and experience muscle fatigue and even rapid heart or irregular heart rates. The same is true for your horse.
Just drinking water may not be enough to replace the lost minerals and this is a more crucial process for the horse, which sweats out more fluids and salts.
If you have ever taken the saddle off a hot sweaty horse and not washed them off or cooled them properly, you can even see patches of salt where the sweat has dried.
Horses also have a greater urine volume than humans and can easily excrete 3 to 4 gallons a day, adding to the loss of fluids and electrolytes.
Research done on horses competing in the Olympics and Endurance races showed that horses may not show the effects of fluid and mineral loss until after they have rested and that if not corrected and the horse not given time to recuperate before being asked to work again, the horse will experience fatigue faster and show greater signs of heat stress with a LOWER rectal temperature than normal.
Considering most carriage tour owners use the rectal temperature of a horse as their guide to whether the horse is nearing heat stress or not, this could be problematic.
In a report entitled Acidosis and Skeletal Muscle Fatigue in horses, by Kennth William Hinchclif, Andris J. Kaneps, and Raymond J George in the journal Equine Exercise Physiology: the science of exercise in the athletic horse, the scientists discovered that dehydration increased stress on the cardio-vascular systems of horses and decreased the horse’s ability to regulate their own internal temperatures.
They state that, “Dehydration decreases exercise heat tolerance such that fatigue occurs at a lower core temperature when compared to exercise undertaken in the euhydratred state.”
Euhydrated, simply means, well hydrated.
Further research showed that older horses tended to overheat when dehydrated in half the time as younger horses.
So, bottom line: fit acclimatized horses can handle slightly higher temperatures than their human contemporaries, but humans are more efficient at cooling themselves through natural means (sweating and capillary cooling).
Horses sweat more than humans and can lose more electrolytes. Even if the sweat is evaporated, horses can lose vital fluids and minerals. They may be able to replace the minerals without getting enough water, or replace the water without getting enough minerals.
Lack of fluids can lead to heart stress and muscle fatigue as well as muscle cramping and colic. Lack of electrolytes can also have a negative impact on the heart and on energy transfer in the body causing fatigue and stress on all body systems.
In short, the answer to the question, “who handles the heat better?”, might be better phrased, how does either manage so that they are not negatively impacted by the heat.
The best way not to be negatively impacted is to stay cool and hydrated. For horses this means standing or light work in the shade, regular water intake, mineral replacement being made available throughout the day (salt licks and free choice mineral blocks and electrolytes in the feed or an added water bucket with electrolytes mixed in), hosing off with cool water and scraping away excess water to encourage evaporation and taking plenty of breaks from work to allow the muscles to recuperate and heart rates to return to normal.
You can test a horse’s hydration rate by pinching the neck skin and seeing how long it takes to return to normal. If it stays in a tent shape for longer than two seconds, that is generally considered a sign of dehydration.
Capillary refill time is also an indicator of how well a horse is coping with the heat. If you press your thumb into the gum of the horse’s mouth and the area stays white for longer than 2 seconds, it could indicate the horse’s blood flow is suppressed (shock) and the heart is not pumping properly. Normal gum color is pale pink for horses.
If it is too hot for you, chances are it is too hot for your horse. Don’t force your horse to work hard during the hottest part of the day. Be kind and considerate and give your four legged friend a break and don’t expect him or her to be a superhero and gallop 20 miles across the desert without stopping like the fictional movie horses. It may look cool on screen, but in reality it can be a real killer.
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