Equine Heat Index Tool

Check the real-time heat index for your location to monitor the risk of heat stress and safeguard your horse’s health.


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Equine Heat Index Guidelines
Little to No Risk
< 80
Enjoy your ride! Your horse can keep its body cool via natural mechanisms.
Slight Risk
81 – 90
You can still enjoy your ride, so long as you follow a proper post-exercise cool-down routine.
Elevated Risk
91 – 100
Use caution. Exercise should be modified and extra cooling measures may be required.
Very High Risk
101 – 110
Use utmost caution. Avoid exercise and use substantial cooling measures.
Extreme Risk
>111
Use extreme caution. Avoid all activity and use vigorous cooling measures even at rest.

 

Disclaimer: The Equine Heat Index Tool (EHIT) provided on this platform is intended as a general reference for educational purposes only and should not be considered veterinary advice. The EHIT is designed to offer information and insights into the temperature and humidity conditions that may impact equine health and well-being.

EHIT calculations and interpretations are based on available scientific data and established guidelines. However, actual weather conditions can be influenced by numerous factors, which may not all be represented in the available index, and data is subject to errors and incompleteness.

Mad Barn makes no warranties or guarantees, either expressed or implied, regarding the accuracy, completeness, or reliability of the information provided. By using the EHIT, you acknowledge and agree that you assume full responsibility for any actions taken or decisions made based on the EHIT results.

Heat Index Guidelines for Horses

Published on: July 12, 2023
Last updated on: July 17, 2023

Keeping Horses Cool in the Summer Heat: When is it Too Hot?

Summer is one of the most exciting times of year for many horse owners and riders. Longer daylight hours mean more time spent in the saddle, with young riders off from school and show season in full swing.

While summer is a busy time for equestrians, it is crucial to prioritize the well-being and safety of both horse and rider, especially when facing severe heat and extreme weather conditions.

One factor that demands careful consideration is the heat index, a measure that takes into account both temperature and relative humidity to determine how hot it feels outside. Checking the heat index is important when determining whether it is safe to ride your horse or whether any special precautions are required.

In this article, we will discuss how to use the heat index to keep your horse safe and share key considerations for the care of your equine partner during hot summer weather.

Understanding the Heat Index

The heat index, also referred to as the “apparent temperature,” measures how hot it feels (perceived heat) by factoring relative humidity into the actual air temperature. This measure provides a better representation of risk of heat-related illness because humidity makes it harder for the body to cool itself effectively.

Humidity levels, or the amount of moisture in the air, directly impact the body’s natural cooling process, including sweat which is the horse’s primary mechanism for dissipating body heat. When the air is saturated with moisture, sweat doesn’t evaporate as quickly or efficiently from the skin, making it feel hotter than the actual air temperature and reducing the body’s ability to regulate its temperature.

Equines are more susceptible to overheating than humans due to their higher proportion of active muscle mass, which produces a lot of body heat. Horses also have a lower body surface-to-mass ratio, meaning they have less surface area through which to dissipate heat via sweat. [9][5]

High heat index values can lead to heat stress and heat-related illnesses for both horse and rider, especially when exercising. Always check the heat index before exercising your horse and modify activities or take precautions accordingly.

How is the Heat Index Calculated?

The heat index is calculated using a combination of air temperature and relative humidity, which measures the amount of moisture present in the air. The formula for calculating the heat index slightly varies across different countries, and it also depends on whether the temperatures are expressed in Fahrenheit (°F) or Celsius (°C).

A commonly used method to compute the heat index in Fahrenheit (°F) is the formula devised by the National Weather Service (NWS) in the United States. [13] This formula requires the following inputs:

  • Air temperature (T): The ambient temperature in Fahrenheit (°F)
  • Relative humidity (R): The percentage of moisture in the air, indicating how saturated the air is with water vapor
Heat Index = -42.379 + 2.04901523T + 10.14333127H – 0.22475541TH – 6.83783 × 10-3T2 – 5.481717 × 10-2H2 + 1.22874 × 10-3T2 + 8.5282 × 10-4TH2 – 1.99 × 10-6T2H2

If the air temperature is given in Celsius (°C), convert this value to Fahrenheit (°F) first to perform the calculation. Note that this formula is designed for temperatures of 80°F or more, and relative humidity values of 40% or more. The heat index is not accurate for lower values.

Also, remember that the heat index is designed for shady, light wind conditions. Exposure to direct sunlight can increase heat index values by up to 15°F.

National Weather Service Heat Index Chart

Figure 1: National Weather Service Heat Index Chart for Humans in Shady Locations [13]

 

Equine Heat Index Chart

Heat index guidelines for exercising horses are similar to those for human athletes, albeit with slightly different temperature thresholds, recommended precautions and activity modifications.

The following heat index chart provides equine-specific protocols for determining when it is safe to exercise your horse as well as appropriate cool-down routines to protect your horse from heat stress.

Heat Index Chart for Horses
Little to No Risk
< 80°F
< 27°C
Enjoy your ride! When the heat index is less than 80°F (27°C), your horse can keep its body cool via natural mechanisms. Your normal post-exercise cool-down routine should be sufficient. Offer fresh water for drinking, perform a quick hosing, and let your horse dry off in a well-ventilated area.
Slight Risk
81 – 90°F
27 – 32°C
You can still enjoy your ride! Be aware that your horse’s cooling mechanisms are slightly compromised when the heat index is between 81 – 90°F (27 – 32°C). However, the risk of overheating remains low. Follow a proper post-exercise cool-down routine to ensure your horse’s temperature returns to normal. Offer fresh water for drinking, hose down your horse, and let them dry off in a well-ventilated area.
Elevated Risk
91 – 100°F
32 – 37°C
Use caution! When the heat index is between 91 – 100°F (32 – 37°C), your horse’s cooling mechanisms are very compromised and the risk of overheating is moderate. Exercise should be modified and additional cooling measures may be required. After exercise, offer your horse fresh drinking water, hose them down, and let them dry off in a well-ventilated area or under fans until your horse’s vital signs normalize.
Very High Risk
101 – 110°F
38 – 43°C
Exercise utmost caution! When the heat index is between 101 – 110°F (38 – 43°C), your horse’s natural cooling mechanisms are ineffective and there is significant risk of overheating. Exercise should be avoided and substantial cooling measures may be required. If your horse must exercise, immediately provide them with fresh drinking water and continuously hose them down in a well-ventilated area until their vital signs return to normal.
Extreme Risk
> 111°F
> 43.5°C
Exercise extreme caution! When the heat index exceeds 111°F (43.5°C), your horse’s cooling mechanisms are ineffective, leading to an extremely high risk of overheating even at rest. All activity should be avoided and vigorous cooling measures are required at all times. Provide your horse with fresh drinking water and keep them sheltered in a well-ventilated area with fans or misters. Consider relocation if a prolonged heatwave is expected. If your horse shows signs of heat stress, continuously hose them down until their vital signs normalize.

 

Equine Heat Index Guidelines

 

Staying Safe When Riding in Hot Weather

In hotter climates or during periods of extreme heat, temperature management, hydration, and proper care are vital to ensure the safety and welfare of both the rider and the horse. Before jumping into the saddle, consider the following: [11]

  1. Monitor the heat index: Before you head out for a ride, check the heat index for your area. Avoid or modify riding when the heat index reaches potentially dangerous levels, usually above 90°F (32°C).
  2. Hydration is key: Ensure that both you and your horse are adequately hydrated before, during, and after riding. Offer your horse water regularly, provide free-choice loose salt and feed electrolytes to replenish those lost in sweat. Take breaks during your ride to allow your horse to rest and drink water.
  3. Time your rides appropriately: Plan your rides during the coolest parts of the day, usually early morning or late evening when temperatures are lower and the heat index is more favorable.
  4. Adjust the intensity and duration of the ride: When the heat index is high, shorten the duration and reduce the intensity of rides to prevent overexertion and excessive sweating. Listen to your horse and be mindful of any signs of fatigue or distress.
  5. Provide shade and ventilation: If possible, choose routes that provide shade, such as wooded trails or areas with buildings. Proper airflow helps horses regulate their body temperature. Ensure that your horse’s stable and turnout areas have sufficient ventilation.
  6. Watch for signs of heat stress: Be vigilant for signs of heat stress in your horse, including excessive sweating, rapid breathing, elevated heart rate, lethargy (fatigue), stumbling, or muscle weakness. If you notice any of these signs, dismount immediately, find shade, and cool your horse down with water.

By carefully monitoring the heat index, modifying your riding routine, and being attentive to signs of heat stress, you can ensure your horse’s comfort and protect them from the risks associated with excessive heat. Ultimately, adopting an informed approach to riding in hot weather will keep both you and your horse safe and healthy.

What to Do if Your Horse is Overheating

If you suspect your horse is experiencing heat exhaustion or heatstroke, it is vital to take immediate action. Keep in mind the five principles of SHADE: [7][11]

SHADE
STOP: Dismount and head towards a shaded, well-ventilated area. Remove as much tack as possible.
HYDRATE: Provide access to cool water for drinking.
APPLY: Apply cooling techniques, such as using fans and hosing down your horse with a continuous water spray, to reduce your horse’s core temperature. When hosing your horse, aim for the large blood vessels in the neck, chest, and between the hind legs to maximize cooling.
DROP: Continue cooling measures until your horse’s rectal temperature drops and vital signs begin to stabilize. Do not stop to sweat-scrape.
ENGAGE: Contact your veterinarian as soon as possible for further guidance and treatment. Prompt veterinary care is essential for managing heatstroke and preventing potential complications or organ damage.

 

Heat-Related Illness in Horses

Heat stress, heat exhaustion and heatstroke are often used interchangeably, but they each represent distinct stages of heat-related illnesses. Below, we will delve into the definitions and differences between these concepts.

  • Heat stress is the physiological strain on the body when exposed to high temperatures or a hot environment. It typically occurs when the body’s ability to cool down through sweating and other cooling mechanisms is challenged.
  • Heat exhaustion is a more serious heat-related condition when the body cannot adequately cool and maintain normal core temperature. It is usually a result of prolonged exposure to high temperatures, inadequate hydration, and insufficient electrolyte balance.
  • Heatstroke is the most severe and life-threatening heat-related condition. It occurs when the body’s core temperature rises significantly due to prolonged exposure to high temperatures or strenuous physical activity in hot conditions. Heatstroke is characterized by a breakdown in the body’s ability to regulate its temperature, leading to multiple organ dysfunction.

Effects of Overheating in Horses

Overheating can have a profound impact on your horse’s health and well-being, potentially leading to central nervous system dysfunction and, in severe instances, even mortality. Consequences of heat exhaustion and heatstroke include dehydration, muscle damage, and organ dysfunction. [9]

Horses with heat-related illnesses often present with excessive fluid loss, resulting in electrolyte imbalances. Disruption of electrolyte levels can lead to the impairment of normal bodily functions (including muscle and nerve function), and give rise to additional complications. [9][7]

Heatstroke also stresses the horse’s vital organs due to increased body temperature, dehydration, and reduced blood flow. These factors can contribute to organ dysfunction and potentially lead to long-term tissue damage if not properly addressed. [9][7]

If your horse is showing signs of overheating, it is important to seek immediate veterinary attention and provide proper supportive care, including cooling measures, rehydration, and close monitoring. Prompt intervention is crucial to minimize negative consequences and support your horse’s recovery.

Signs of Heat-Related Illness in Horses

In hot and humid conditions, it is important to be vigilant for signs of heat stress and heatstroke in your horse and respond promptly. Exercising your horse in hot weather demands additional vigilance.

Here are some of the most common signs of heat-related illness in horses: [9][7]

  1. Excessive sweating or lack of sweating: Heatstroke can manifest in horses as either excessive sweating or, in severe instances, a complete absence of sweating (anhidrosis). If your horse stops sweating in hot weather, this is a serious indication of heatstroke.
  2. Rapid and shallow breathing: Horses with heatstroke often exhibit rapid, shallow breathing, panting, or increased respiratory rate. Your horse may show signs of respiratory distress.
  3. Elevated heart rate: During heatstroke, a horse’s pulse can be significantly increased.
  4. Elevated body temperature: Horses experiencing heatstroke will exhibit a noticeably elevated body temperature, typically measured as a rectal temperature above 105°F or 41°C. However, rectal temperature alone is insufficient to diagnose heatstroke, as other factors such as routine exercise and stress can temporarily increase body temperature.
  5. Neurological abnormalities: Heatstroke can cause your horse to become weak, lethargic, and uncoordinated. They may appear dull, listless, or disoriented. Their performance and response to stimuli may also be noticeably decreased. In severe cases, this can progress to recumbency (lying down and unable to rise) and seizures.
  6. Dark urine: Dehydration resulting from heatstroke may lead to concentrated urine, which appears darker in color than usual. Dark urine may indicate compromised kidney function due to severe fluid loss.
  7. Red or congested mucous membranes: The mucous membranes inside your horse’s mouth, gums, and eyes may appear reddened or c