Summer brings longer days, more riding time, and unfortunately, an increased risk of overheating for our equine companions.

While most horse owners understand that water is essential, the science behind proper summer hydration goes far beyond simply filling water troughs.

Understanding how horses regulate body temperature and lose crucial minerals through sweat can mean the difference between a healthy, comfortable horse and a veterinary emergency.

The Physiology of Heat: How Horses Stay Cool

Horses face unique challenges when it comes to cooling themselves.

Horses naturally cool themselves by sweating, with the sweat evaporating from the skin surface to create a cooling effect.

However, less sweat evaporates during times of high humidity, making hot, humid days particularly dangerous.

The numbers are staggering when you consider how much horses sweat.

A horse that is working hard in a hot environment can lose 2 to 4 gallons of sweat per hour.

To put this in perspective, an average-sized mature horse will drink between 5 to 10 gallons per day at a moderate temperature of 68°F.

But as temperatures increase, the amount of water consumed increases significantly, ranging between 11 and 15 gallons for the same horse at 86°F, and that same horse exercising moderately in 95°F heat will consume 19 to 24 gallons of water!

 

When Heat Becomes Dangerous

Prolonged exposure to high temperatures can result in heat stress, heatstroke and problems such as dehydration, muscle spasms and colic.

Warning signs every horse owner should recognize include:

• High rectal temperature (103 – 107°F or 39.5 – 41.5°C)
• Anything above 50 breaths per minute
• Very rapid heart rate at rest (more than 60 beats/min)
• Profuse sweating or, worse, when horses stop producing sweat altogether

Heat stress becomes particularly concerning when the horse’s body temperature exceeds 40.5°C (105°F), as this can affect the blood supply to the muscles and organs. Prolonged or severe heat stress may lead to heat stroke or even brain damage.

Young foals tend to be more prone to heat stress and dehydration, requiring extra vigilance during summer months.

When heat stress is detected in horses of any age, body temperature can be decreased quickly by hosing them down with cool water and getting them to a location with good air movement.

The Critical Role of Electrolytes

Here’s where many well-intentioned horse owners make a crucial mistake: they focus solely on water replacement.

The reality is that water alone cannot result in adequate hydration.

When horses sweat, they don’t just lose water – they also lose electrolyte minerals, specifically high levels of sodium, potassium, and chloride.

Horses’ sweat is hypertonic, meaning it has a higher concentration of electrolytes compared to blood.

This is why simple water replacement falls short. Effective hydration requires the supplementation with electrolytes, together with adequate amounts of water.

 

Practical Summer Hydration Strategies

Environmental Management

• Avoid exercising your horse when the heat index (temperature + relative humidity) is over 150 (learn more about heat index and equine heat stress from the University of Minnesota Extension)
• Working horses should be offered cool, fresh water at least once an hour during extended periods of exercise
• Provide ample shade outdoors and good ventilation in the barn

Hydration Enhancement

• Soaking your horse’s hay and grain is an excellent way to increase hydration – one flake of soaked hay can absorb 1–2 gallons of water
• For an average 1,100-pound horse, feed at least 2 tablespoons (30 grams) of salt per day with their feed and provide plain, loose free-choice salt all the time
• Ensure constant access to clean, fresh water by changing the water frequently and cleaning water buckets daily

 

Emergency Response

If you suspect heat stress, stop riding your horse, find a shady spot to rest, and call your horse’s veterinarian, as the situation may quickly become an emergency.

Starting with the feet and legs, gradually wet the horse’s entire body, including the head, with cool water.

The Bottom Line

Summer hydration is a complex science, not simple common sense.

Dehydration is common in equine disciplines and can be avoided, thus promoting equine wellness, improved performance and enhanced horse and rider safety.

Understanding the physiology behind heat stress and the critical role of properly formulated electrolyte replacement can help keep your horse healthy, comfortable, and performing at their best throughout the summer months.

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