Helping Horses Beat the Heat

Jun 14, 2022

Summer heat and humidity are challenging for both horses and horse owners. Helping horses cope with the heat is important for both their comfort and optimum athletic performance. You might be surprised to learn that horses are less tolerant of high temperatures than humans. This is because horses have a larger body mass to surface area ratio than humans, which means they have to dispel more heat per square inch of skin than humans in hot conditions. In this article, we’ll discuss how horses regulate their body temperature and how we can manage performance horses when working in hot, humid weather.
Animals’ bodies function best within a very narrow temperature range. Thermoregulation is the process by which the body maintains optimum core temperature (99-101°F for adult horses). Heat is produced as a result of many biological functions, including muscle contraction and metabolism. Excess heat must be transferred from the horse to its environment to maintain body temperature. Heat is transferred from one object to another by four primary mechanisms: conduction, convection, radiation, and evaporation. Conduction occurs when heat is transferred from a warmer object to a cooler object through direct contact; for example, when you touch a hot stove, heat from the stove is transferred to your hand. Convection occurs when heat is transferred through a liquid or gas, such as the loss of body heat to the atmosphere in cold weather; air movement, via wind or fans, increases the rate of convective heat loss. Radiation is the transfer of heat from one object to another without direct contact; we can feel this effect when we step outside on a bright, sunny day. Evaporation occurs when heat transforms a liquid to a gas; sweating and panting are both examples of evaporative heat loss mechanisms in animals. Horses produce copious amounts of sweat, especially during exercise, as an effective means of reducing their body temperature. Some horses, however, suffer from a condition called anhidrosis. Anhidrosis causes sweat glands to become less responsive to adrenaline; while most horses with anhidrosis retain some limited ability to sweat, this ability is greatly reduced, especially in humid conditions. It is especially important that these horses be monitored closely in hot weather to prevent hyperthermia.
How Hot is Too Hot?
If horses are less tolerant than humans, does that mean we shouldn’t ride our horses during the summer? Of course not! However, you should be mindful of the extra stress horses are under during hot, humid weather so that you can make sure your horse stays as comfortable as possible. A simple measurement of comfort in hot weather is the heat index system. A heat index is calculated by adding the air temperature (in °F) and the relative humidity (in %). The heat index is similar to a wind chill factor in winter weather; it gives us information about how comfortable outdoor conditions are likely to be. While there are no hard and fast rules about heat index values and equine comfort, there are some generally accepted guidelines that are useful for horse owners (see Figure 1). Keep in mind that, like people, horses do become acclimated to hot, humid weather conditions over time. For example, a heat index of 145 might cause noticeable fatigue or loss of performance in late May while appearing to have no effect at all on the same horse in late July. It is important to keep this in mind when preparing performance horses for competitions or events. You should gradually acclimate the horse (and yourself) to working during the heat of the day if it is going to do so during the competition, rather than only riding during cool morning hours at home and then expecting the horse to perform at peak level in the mid-afternoon heat on the big day.
Heat Index Caution Level
< 130 Exercise as normal. Most horses will not be affected by heat stress.
130 – 150 Horses may require additional cooling out following exercise. Pay attention to signs of excessive fatigue/stress.
150 – 180 Monitor horses closely; a reduced workload may be required. Extra cooling out effort required due to lack of evaporative efficiency.
> 180 Generally considered unsafe conditions for exercising horses. Monitor all horses, even at rest/pasture, for signs of heat stress.
Figure 1. General heat index guidelines for exercising horses
Does My Horse Need an Electrolyte Supplement?
As we’ve already discussed, horses sweat as a primary means of reducing body temperature, and horses are capable of producing very large volumes of sweat. A galloping horse, for example, can lose more than 10 gallons of sweat per hour of exercise! Along with water, horses also lose important nutrients in sweat. Electrolytes are minerals that play important roles in fluid balance throughout the body; the primary electrolytes lost in large quantities via sweat are sodium, potassium, and chlorine. Under normal conditions, horses receiving a balanced diet will easily replace the electrolytes lost in sweat, with the exception of sodium and chlorine. Sodium and chlorine are most commonly provided to horses on a free-choice basis in the form of a salt block. It is important to monitor the salt block to ensure the horse is taking in adequate salt because some horses do not like the abrasive texture of the salt block. On average, an adult horse should consume around 2 ounces of salt per day. If you find that your horse is consistently taking in less than this, consider providing free-choice loose salt or adding salt to the horse’s feed instead. Horses performing prolonged exercise in the heat, such as eventers and endurance horses, will lose significant amounts of electrolytes and will likely require supplemental electrolytes to replace these losses. The horse should be acclimated to the supplement ahead of the competition so that it doesn’t refuse the supplement when mixed into its feed or water.
Cooling out a Hot Horse
When caring for very hot horses, the primary goal is to reduce their body temperature as quickly as possible. The best way to do this is by repeatedly applying cold water to the horse, ideally while either walking the horse or standing it in front of a fan. This technique maximizes multiple cooling mechanisms: conduction (cold water absorbs heat from the horse’s skin), convection (moving air allows more heat loss from the horse than still air), and evaporation. Scraping the excess water from the horse between water applications is not necessary and will actually slow the rate of heat loss, as both conductive and evaporative losses will be reduced if the water is manually removed from the horse’s coat. The horse should be allowed access to water throughout the cooling down process; if the horse has been exercising and sweating heavily, offer electrolyte supplementation via a separate water bucket as well.
We can’t completely eliminate the negative effects of very hot weather, but careful management can minimize these effects and help our horses feel and perform their best. Keeping your horse hydrated, paying close attention to signs of stress, and working to cool out a hot horse as quickly as possible are important aspects of managing performance horses during the summer months.
For more content like this, check out the latest issue of the Cooperator.

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