With higher temperatures in the summertime, horses are prone to heat stress. This can contribute to an increased risk of colic, ulcers, weight loss, fatigue and dehydration during this time of year. [1]

Horse owners should be vigilant for signs your horse is overheated, which include excessive sweating, lethargy, elevated breathing and heart rate, and decreased appetite.

If your horse appears at risk of heatstroke, contact your veterinarian right away and cool them down with fans and cool water.

You can keep your horse safe and comfortable in hot weather by ensuring they are drinking enough water, replenishing electrolytes, avoiding intense exercise during peak heat, and keeping them out of direct sunlight for long periods.

Follow the 14 feeding and management tips in this article to support your horse’s well-being all summer long. Consult with our equine nutritionists for help with formulating your horse’s diet through the summer.

Horses in Hot Weather

Horses are extremely efficient at producing heat through digestion and muscular activity. When horses eat forage, microbes in the gut break down cellulose and hemicellulose. This process of microbial fermentation generates heat that needs to be dissipated. [2]

The horse’s gut is designed to constantly digest plant fibre. But this process can work against your horse in extreme heat, compounding the risk of heat stress and associated issues.

Additionally, horses in work generate heat through their working muscles. [2] This makes it harder for horses to thermoregulate when exercising in hot and humid environments.

How Horse Stay Cool

For all mammals, core body temperature is maintained in a narrow range by continuously balancing heat production with heat loss. A stable core body temperature is maintained by regulating: [15]

  • The body’s rate of heat production
  • The transfer of heat to the external environment
  • The efficiency of evaporative cooling

The rate of heat production in the body can be adjusted by increasing or decreasing metabolic rate. However, both extreme cold and extreme heat result in a faster metabolic rate as the body activates various systems to try to regain a normal core temperature.

There are 4 main ways that horses can lose heat to the environment:

1) Conduction

Conduction involves direct contact between the skin and a cooler surface, such as cool water applied to the skin.

This process is more efficient with greater temperature differences between skin and the other surface. It is impaired by insulating materials such as a thick coat.

2) Convection

Convection refers to heat lost to the surrounding air. This process is most efficient if the warmed air is moved and replaced by cooler air which occurs when the horse is running or when they are standing in windy air.

This heat transfer to air can also occur in the respiratory tract when they breathe in cool air.

3) Radiation

Radiative heat loss refers to electromagnetic radiation emitted or absorbed at the skin. The most common form is a gain of heat from sunlight which can contribute up to 15% of heat gain in a horse exercising in sunny conditions. [16]

When a horse’s internal body temperature increases above baseline, blood vessels in the skin expand (vasodilate) to enable heat to dissipate into the atmosphere via convection and radiation.

This cooler blood then travels to the internal organs and muscles, reducing internal temperature. [3]

4) Evaporation

This is the most important form of cooling for horses and many other mammals that can sweat.

This involves evaporation of sweat from skin and water exhaled from the respiratory tract. The water droplets hold heat which is lost into the surrounding air when the liquid evaporates.

Sweating is activated by hormonal signals (ephinephrine) that increase during exercise and stress. It is also activated by increased core body temperature which is sensed by thermoreceptors in the skin, abdomen, skeletal muscle and brain.

It is estimated that 1 L of sweat can dissipate 580 calories of body heat which is approximately the amount of heat generated in 2 minutes of high-intensity exercise or 6 minutes of moderate-level exercise. [15][17]

Considering that an exercising horse can lose 10 – 15 L of sweat per hour, sweat provides a major avenue for dissipating heat in the horse.

In low- to mid-humidity conditions, sweat evaporates and cools the skin as well as blood close to the surface. [3]

Extreme Heat & Humidity

This cooling process becomes less efficient in extreme heat and humidity. When temperatures and the humidex are high, sweat cannot evaporate into the air.

The humidex is an index of the humidity in the air, measuring the moisture held in the atmosphere. When the air is already holding an abundance of water molecules, water does not evaporate as quickly.

This means that your horse cannot dissipate as much heat through sweating, impairing the cooling systems of the horse and increasing the risk of heat stress.

Heat Stress in Horses

Heat stress (sometimes called heat exhaustion) is an umbrella term for symptoms caused by a sustained high internal body temperature. Signs of heat stress include: [1]

  • Profuse sweating or less sweat than expected
  • Rapid breathing
  • Signs of dehydration such as loss of skin elasticity, tacky gums, sunken eyes, and reduced urine output
  • Rapid heart rate that does not resolve with rest
  • Muscle weakness
  • Extremely hot skin
  • Colic
  • Weight loss
  • Poor appetite or reduced feed intake
  • Gastric ulcers
  • Fatigue or lethargy
  • Heatstroke

Some horses are particularly susceptible to heat stress because they cannot adequately regulate their temperature in hot weather. This includes young foals, obese horses, older horses with PPID, and horses with anhidrosis (an inability to sweat).

Heat stress is clinically diagnosed by taking the rectal temperatures of the horse. Temperatures above 39.5oC (103oF) indicate heat stress. [13]

Rectal temperatures are typically lower than the horse’s actual core body temperature but are useful as a diagnostic tool.

If a rectal thermometer is not available, observing behaviours such as elevated respiratory rate and flared nostrils can be used as indicators of heat stress. [19]

If you think your horse is experience heat stress or exhaustion, it is critical to reduce their body temperature gradually until their internal temperature is with a normal range (99o to 101oF or 37.5o to 38.5oC) to avoid heatstroke.

Heatstroke

If heat stress devolves into heatstroke, horses can experience permanent internal organ damage or death. Signs of heatstroke include:

  • Dehydration
  • Extremely elevated internal temperature
  • Altered behaviour, either listless or panicky
  • Thick, dark urine
  • Stumbling
  • Muscle spasms
  • Seizures [4]

Heatstroke is clinically diagnosed with a rectal temperature greater than 40.5oC (105oF). Horses with heatstroke will also have a respiratory rate of greater than 40 breaths per minute and a heart rate of greater than 60 beats per minute. [13]

Heatstroke is a veterinary emergency. Call your veterinarian immediately and start cooling your horse right away to minimize the risk of long-lasting adverse effects.

Cooling your Horse

If your horse is experiencing heat stress or heatstroke, you can cool them down safely with the following strategies:
[13]

  • Move the horse indoors or into a shaded area and out of direct sunlight
  • Use fans or a misting device
  • Spray the horse’s head, back, and rump with cool water
  • Use ice water in cases of extreme heat
  • Provide fresh, cool water to encourage drinking

While rapid cooling can cause muscle cramping to occur, research shows that applying ice water to the skin can be used safely to cool down a horse. [13]

Your horse’s veterinarian may also administer IV fluids and electrolytes to combat dehydration.

14 Tips for Caring for your Horse in Hot Weather

Horses have evolved to live in some of the hottest regions of the world. Feral herds of the Namib Desert horse live in Namibia where daytime temperatures in the summer can exceed 45°C (113 °F).

Some horses are better suited to hotter climates (i.e. Arabians and Marwaris) while other breeds are less suited (i.e. Clydesdales and Icelandic Ponies).

Regardless of breed, you can ensure your horse is comfortable even in the hottest and most humid environments with the right feeding and management strategies.

Below, we outline 14 tips for caring for your horse in hot weather to keep them happy and safe from heat stress.

1) Encourage Adequate Water Intake

During particularly hot, humid days or intense exercise, horses can produce up to 15 litres of sweat per hour. If this water loss is not appropriately replaced, your horse can quickly become dehydrated. [4]

Encouraging water consumption helps to replace water lost through sweat and urination. Drinking water that has a lower temperature than your horse’s internal temperature can also help cool the body.

As the famous saying goes, “You can lead a horse to water, but you can’t make them drink”. However, you can encourage your horse to drink more water by:

  • Providing constant access to fresh, clean water
  • Offering water at a temperature of 45o to 65oF
  • Placing water in areas where your horse naturally spends their time (i.e. close to food or their favourite shady spot)
  • Providing multiple water sources to herds so that even horses low in the social hierarchy have constant access
  • Cleaning buckets or water troughs regularly
  • Providing water in blue buckets, which have been shown to increase consumption
  • Adding safe but tasty additives to water such as apple juice, small amounts of jello powder, or flavoured electrolytes

Giving your horse constant access to fresh cool water is the best way to ensure a happy, hydrated horse in heat.

2) Ensure Adequate Salt Consumption

Salt has a number of important roles in the horse’s body, but one of the most important is promoting thirst.

In one study, doubling the salt in a horse’s daily ration from 50 mg/kg to 100 mg/kg body weight resulted in a 53% increase in water consumption. [14]

Feed your horse 2 tablespoons (30 grams) of salt per day with their feed and provide plain, loose free-choice salt at all times.

Loose salt is recommended over salt or mineral blocks because horses do not obtain enough salt from blocks.

3) Consider Electrolyte Supplementation

When your horse sweats, they don’t just lose water. They also lose electrolyte minerals – specifically high levels of sodium, potassium, and chloride. [5]

Horse’s sweat is hypertonic, which means that it has a higher concentration of electrolytes compared to blood. This makes horses particularly susceptible to excessive electrolyte loss in hot weather or with exercise.

If electrolytes are not replaced promptly, your horse can experience:

  • Fatigue
  • Muscle wasting
  • Weight loss
  • Muscle cramps
  • Reduced sweating
  • Slow recovery time following exercise

In extreme cases of electrolyte imbalance, horses can experience heart palpitations and seizures. [6]

When temperatures are high, and especially when exercising your horse in hot weather, feed an electrolyte supplement to replenish levels and restore electrolyte balance.

Performance XL: Electrolytes Equine Supplement

Performance XL: Electrolytes