How Dehydration Impacts Your Horse's Performance

Dehydration can greatly impact your horse's performance and health, especially during the warm summer months in the UK when the climate can occasionally become dry and hot. Although prolonged dry spells are rare, being prepared is essential to keep your horse safe and performing at their best. Ensuring constant access to fresh, clean water is the foundation of good hydration, whether at home or competing.

1. Ensuring Your Horse Always Has Access to Fresh Water

Horses should have free access to clean water at all times, especially during hot and dry periods. When competing in events during summer, never restrict water availability. Horses that are fussy drinkers and hesitant to drink unfamiliar water might benefit from bringing their own supply.

A helpful trick is flavouring the water with a small amount of apple juice or fresh mint, which some horses find enticing. Additionally, there are safe, specifically formulated electrolyte products available that can encourage reluctant drinkers to hydrate appropriately.

2. Feeding Strategies for Horses That Don't Drink Enough

If your horse doesn't drink enough, you might consider feeding them haylage rather than hay. Haylage contains a higher moisture content, which can help improve hydration and may reduce the risk of colic. If haylage is cost-prohibitive, soaking regular hay before feeding is a more affordable and effective alternative to increase moisture intake.

3. The Importance of Cooling Down After Exercise

Immediately cooling your horse after exercise on hot days is vital to reduce excessive sweating and fluid loss. Properly cooling down helps maintain hydration and lowers the risk of heat-related illnesses that can severely compromise a horse's wellbeing and performance.

4. Provide Shade During Summer Competitions

Summer competitions and events are wonderful opportunities, but always ensure your horse has access to shade when tied up or resting. Standing in direct sunlight causes water loss simply through heat exposure, so shade is a crucial component in maintaining hydration levels and comfort.

5. Using Electrolytes to Support Hydration

Electrolytes are important to replace salts lost through sweat during exercise. Carry electrolyte supplements in your competition kit to help replenish these vital minerals, supporting fluid balance and helping your horse recover and perform better.

6. How to Recognise Dehydration in Your Horse

Detecting dehydration early can prevent serious health issues. While the most accurate test requires a blood sample to measure plasma protein and red blood cell concentration, there are practical signs to watch for at home:

• Dark-coloured urine or infrequent urination
• Red and congested mucous membranes

7. Why the Skin Pinch Test Is No Longer Recommended

Traditionally, the skin pinch test was used to assess hydration by pinching the skin and measuring how long it took to return to normal. However, this test can be misleading and is no longer encouraged as a reliable method.

8. Prevention: The Best Approach to Dehydration

Prevention is crucial. Always provide free access to fresh water and avoid riding during the hottest parts of the day to minimise sweating. When exercising during warm weather, ensure you cool your horse promptly to prevent excessive sweat loss and dehydration.

9. Responsible Handling During Summer Events

At events and shows, your horse may face unfamiliar conditions that affect hydration. Be proactive in bringing your horse's preferred water, flavour it if necessary, and provide shade and electrolyte supplements. These steps help you care responsibly for your horse's health and performance during busy summer schedules.

Though the UK doesn't often experience extreme heat waves, summer conditions can still pose a dehydration risk to horses, impacting performance and health. By following these 9 practical tips—including constant access to clean water, feeding adjustments, effective cooling down, and electrolyte use—you can safeguard your horse from dehydration. When competing or out in the heat, take extra care to ensure your horse remains well hydrated and comfortable, helping them perform at their best all summer long.

For those looking to provide for their horses with additional or specialised equipment, always source through reputable suppliers and be aware of your horse's individual needs to promote long-term welfare.

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What Causes Dehydration in Horses?

Understanding the causes of dehydration helps you take the right preventative action. The most common cause is excessive sweating during hard work or hot weather. A horse can lose up to 12 litres of sweat per hour during strenuous exercise — and unlike human sweat, equine sweat is hypertonic, meaning it contains a higher concentration of electrolytes than the blood. This means horses lose vital salts (primarily sodium, chloride, and potassium) every time they sweat, not just water.

Diet is another significant factor. Hay has a moisture content of around 15%, compared to 30–50% for haylage and up to 80% for fresh grass. Horses on a hay-only diet — such as those on box rest or prone to laminitis — are therefore at greater risk of dehydration and need to drink more to compensate. Stress, illness, travelling, and competing away from home can all reduce a horse's willingness to drink, even when water is freely available. Herd dynamics can also play a role: in groups, a dominant horse may guard the water source and restrict access for others.

Dehydration can occur at any time of year, not just in summer. Cold water in winter can deter horses from drinking sufficiently, and stabled horses may drink less than those at pasture. Monitoring water intake year-round — not just during heatwaves — is essential for responsible horse management.

How to Rehydrate a Dehydrated Horse

If you suspect your horse is dehydrated, act promptly but carefully. Offer clean, fresh water immediately and allow the horse to drink at its own pace. Avoid forcing large volumes in one go — for a mildly dehydrated horse, offering water at 10-minute intervals until thirst is quenched is a sensible approach. If your horse refuses plain water, try offering a soaked feed or mash, which provides fluid alongside familiar flavours and nutrients that encourage intake.

Electrolyte supplementation is important when rehydrating, but there is a key caveat: giving a large, concentrated dose of electrolytes without sufficient water can worsen dehydration in the short term, as the body pulls water from tissues to process the salt load. Electrolytes are best given gradually, added to water or feed in small amounts. Most commercial equine electrolyte products include dosing guidance for rehydration scenarios.

For a horse showing signs of moderate to severe dehydration — marked lethargy, sunken eyes, very dry gums, or signs of colic — contact your vet immediately. Intravenous fluid therapy administered by a vet is the most effective treatment for serious cases and can be life-saving when dehydration has progressed beyond what oral rehydration alone can address. Recovery time depends on the severity: mild dehydration may resolve within a few hours, while a heavily sweating competition horse may take a full day or more to return to normal hydration levels.

Frequently Asked Questions

How do you tell if a horse is dehydrated?

Key signs include dark or reduced urine output, dry or tacky gums (press a finger to the gum — it should return to pink within 2 seconds), lethargy, dull eyes, and poor performance. The gum capillary refill test is more reliable than the skin pinch test for assessing hydration at home.

How long does it take to rehydrate a horse?

A mildly dehydrated horse can recover within a few hours with access to water and electrolytes. A heavily sweating horse that has lost significant fluid during competition may take 24 hours or longer to fully rehydrate. If a horse is not improving after several hours of free access to water, contact your vet.

Can dehydration cause colic in horses?

Yes. Dehydration reduces the moisture content of gut contents, which can cause them to become firm and impacted — a condition known as impaction colic. This is one of the more serious complications of dehydration in horses and can require veterinary treatment. Ensuring consistent water intake, particularly in horses fed primarily on dry hay, is one of the most effective ways to reduce colic risk.

What is the best electrolyte for horses?

Look for a product where the primary ingredients are actual electrolytes — sodium, chloride, potassium, magnesium — rather than sugar or glucose, which do not improve absorption. Choose a balanced, isotonic formulation designed specifically for horses. Your vet or an equine nutritionist can recommend an appropriate product for your horse's workload and individual needs.