Horse Hydration: Your Questions Answered

We consulted two equine nutritionists to answer your burning questions about horse hydration. Here’s what you need to know.

Posted by Alexandra Beckstett, The Horse Managing Editor | Jun 3, 2019 | Article, Basic Care, Horse Care, Nutrition, Nutrition Basics, Seasonal Care, Vital Signs & Physical Exam, Water & Electrolytes

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We consulted two equine nutritionists to answer your burning horse hydration questions.

Water is the fuel that keeps all living creatures’ bodies functioning. In horses, it’s a crucial nutrient for digestion and thermoregulation, among other life-supporting functions. However, there’s more to horse hydration than simply providing them constant access to clean water. In this article we’ve called on Kristen M. Janicki, MS, PAS, an equine nutritionist based in Nicholasville, Kentucky, and Mary Beth Gordon, PhD, an equine nutritionist and director of equine research at Purina Animal Nutrition, to answer your most frequently asked reader questions about hydration. In no particular order, here’s (almost) everything you need to know about watering horses:

1. How long is too long for a horse to go without water?

Although horses’ bodies can tolerate a lack of water for extended periods, dehydration from water restriction can quickly become fatal. Janicki recommends seeking veterinary help if it’s obvious (based on clinical signs mentioned in No. 5, along with untouched water sources) a horse hasn’t been drinking for two days. “After three to four days, the horse’s organs will begin to shut down, which can result in irreversible (organ and tissue) damage,” she explains.

Water intake, however, is not just about drinking. “Horses on pasture (which has a high percentage of moisture) will sometimes drink little to no additional water,” Gordon explains. “The more dry feedstuffs fed to the horse (such as hay), the more water they will drink.”

She adds that horses also naturally generate “metabolic” water as a result of breaking down protein, carbohydrates, and fat. “This does not provide a large amount of water, but does contribute to the horse’s daily balance,” she says. “All of these things may change the horse’s demand for water. Always follow good basic horse keeping rules and have fresh, potable water available at all times.”

2. How do I encourage my horse to drink?

Both of our sources agree that the easiest way to encourage drinking is to provide your horse with fresh, clean, palatable water at all times. “Frequently checking, scrubbing, and refilling water troughs and buckets is part of the nitty-gritty of horse keeping,” Gordon says.

Other ways to up your horse’s intake include soaking hay and providing salt via salt blocks, loose salt top-dressing on feed, or a salt supplement. “Correct sodium balance in the horse is necessary for proper thirst response and body water equilibrium,” Gordon explains. 

3. What temperature water do horses prefer to drink?

There is evidence that horses prefer lukewarm (20°C or 68°F) water, especially during cold weather, Janicki says. For instance, researchers have shown that pony stallions drank 38-41% less water when it was near frozen compared to when it was 66°F. Yet, when kept indoors at warm temperatures, they drank the same amount of both 32°F water and 66°F water.

4. Can a horse drink too much water? 

A horse can, in fact, drink too much water, particularly if he suffers from certain health conditions, such as equine Cushing’s disease. Such ailments can cause a horse to exhibit polydipsia, or excessive drinking behavior.

“Excessive water intake can cause stress on the kidneys as they eliminate the excess water and can also dilute the electrolytes in the horse’s body, decreasing its ability to regulate temperature,” Janicki explains.

Healthy horses, however, typically don’t drink beyond their body’s capacity, says Gordon: “In research we conducted looking at water intake from adding sodium to diets, no horse drank beyond what was considered normal for their body weight or based on weather conditions. We’re usually more concerned about the opposite: horses not drinking enough water.”

5. What are signs of dehydration, and what do I do if my horse becomes dehydrated?

Becoming familiar with your horse’s normal vital signs (TheHorse.com/EquineHealthSigns) is one way you can prepare to detect dehydration. Clinical signs include an elevated heart rate or pulse (28-40 beats per minute is normal for an adult horse), changes in gum color and feel (bubblegum pink and moist are normal), and decreased skin elasticity (detectable via a skin pinch test, in which the skin along the neck in front of the shoulder should retract back to normal in less than two seconds when pinched and released). According to the American Association of Equine Practitioners (AAEP), changes to these vital signs occur when the horse is 4-6% dehydrated. Horses typically display visual signs such as sunken eyes and a tucked-up appearance to the abdomen when dehydration levels approach 8-10%.

“Most of the time, dehydration can be fixed by offering clean, palatable water,” Janicki says. “In cases where the horse is 8-10% dehydrated, you will need to call a veterinarian to administer fluids.”

6. On a very hot day, how long would it take for a horse to become dehydrated?

“An idle horse requires approximately 5 L water/100 kg body weight,” Janicki says. “Typically, for a 1,100-pound horse, that would be around 25 L (6.6 gallons) of water per day. This is based on research done on horses kept at a thermoneutral temperature range  (-15-10°C or 5-50°F), which is considered to be the temperature a horse maintains its own body temperature with little or no energy expenditure.”

How long it takes for a horse to become dehydrated depends on many individual factors affecting hydration status in hot weather, such as diet, work, pregnancy, lactation, and age. 

The good news is that in two studies Gordon and colleagues performed recently, they saw a positive link between ambient temperature and water intake. “If temperatures are rising, horses will drink more water to maintain hydration status and offset sweat losses,” she explains. “Therefore, (how long it takes for a horse to become dehydrated) partially depends on the availability of water for horses to rehydrate on a very hot summer day.”

In another study, Geor et al. demonstrated that horses exercised at high temperatures (33-35°C or 91-95°F) and high humidity (80-85%) increased their water intake 79% for four hours. 

7. Can certain health conditions impact a horse’s water intake?

Basically, any health condition that decreases feed intake can also lessen water intake, says Gordon. And if a horse suffers from diarrhea for any reason, he can become dehydrated easily, even if drinking normal amounts of water, says Janicki.

On the other end of the drinking spectrum, “horses with uncontrolled glucose/insulin may drink and urinate more,” Gordon says. And, as mentioned, horses with Cushing’s disease can develop polydipsia.

Diet can also affect water consumption. “High levels of fiber (hay), salt, potassium, and protein in the diet can cause excessive water intake,” Janicki notes.

8. How can I keep my horses hydrated while competing or traveling?

Janicki suggests making frequent stops (every two to three hours) to offer your horse water when traveling. This will help him not only stay hydrated but also tolerate traveling for long periods of time.

Gordon says owners can also offer their horses soaked hay or a compressed hay product: “It masks the taste of ‘foreign’ water and helps ensure the horse remains hydrated.”

During competitions or trail rides, offer your horse water whenever possible. “(Horses) should be able to drink as much as they want, unless certain medical conditions prevent this from happening,” Janicki advises. In such cases, work with your veterinarian to determine how much water to offer and how frequently. 

9.  Immediately after an intense workout, should I taper my horses’ water intake or should I allow them to drink all they want, all at once?

Similar to the response to the previous question, a horse should be allowed to drink as much as he wants anytime after performing an intense exercise bout.

Although some owners have reservations about giving a horse free access to water before he “cools down,” Gordon points out that Schott et al. have demonstrated in research studies that horses do not drink beyond their stomach capacity in the first few minutes following intense exercise.

“Water does not need to be withheld,” she says. “Use ambient temperature or ‘hose-cold’ water, and train horses to drink salt water after intense exercise to help replenish water and electrolyte requirements. Also provide clean water at the same time.”

10. Why are some horses so picky about their water sources?

Horses are very sensitive to the smell and taste of water and feedstuffs, says Gordon, and there can be many explanations as to why a horse refuses to drink from a certain water source. Janicki explains that water sources have varying pH levels and, more importantly, total dissolved solid (TDS) levels. “Palatability is affected most by TDS values, which measure the amount of ions in the water source,” she says.

Water hardness (which can be due to high calcium, magnesium, sodium, and potassium levels) also affects palatability. 

If your horse turns up his nose at water when traveling or competing, Janicki suggests taking water from home with you and making it available so your horse will not become dehydrated.

11. I often ride in the desert where there are no water sources. How long and hard can I ride my horse before he needs a chance to drink?

Our sources do not suggest taking long, hard rides in the desert without water sources, unless you’re completing an endurance event. “Endurance riders typically provide water at all times before the ride,” Janicki says. “Soaking hay or hay cubes before the ride will help with fluid balance. Do not provide grain within four hours of (before) the ride, as this may dehydrate a horse quicker. Offering electrolytes before and after the ride in water will help with electrolyte losses and fluid intake.”

12. When trail riding, what kind of natural water sources are safe for horses? What are the signs that a natural water source might not be safe?

Again, clean, fresh water is the best water for horses. Janicki suggests examining a potential water source carefully before allowing your horse to drink from it, considering its clarity (rainfall and runoff decrease clarity), odor (which can indicate unclean water, potentially impacting palatability), temperature (since extremely cold or warm water affects palatability), and color (which does not necessarily affect water quality, so use this factor in combination with the others—i.e., don’t let your horse drink from mirky, moldy-smelling water that is also green).