Preventing Dehydration in Horses


Horse Health: Sponsored by Cornerstone Equine Veterinary Services Keeping horses hydrated during extreme heat.

We all know the old saying “you can lead a horse to water,” but what is the modern take on horses and water? This summer has seen most days with above average temperatures across the mid-south. These temps combined with wide spread draught, can leave horses vulnerable to dehydration. Equines need 1/2 to 1 gallon of water daily per 100 pounds of body weight. For the average 1,100 pound horse that translates to 5.5 to 11 gallons of water every day. This amount increases with hot weather, activity/exercise, medical conditions, lactation, diet (protein requires water to be metabolized), and whether they are housed in dry lots or green pastures.         

A full water trough doesn’t mean your horse is well hydrated. Several factors can affect your horse’s desire to drink. Horses drink best when the water is between 45-65F. Our regional weather hasn’t had night temps as low as 65F in months. And, horses also don’t like dirty water. Dumping your water trough, scrubbing and refilling it several times a week will encourage your horse to drink. Some horses can be finicky about drinking when away from home, especially if the water is city water with chlorine. Filters can be attached to your hose to help horses drink when on the road. Make it a point to check your horse’s water at least twice a day during these extra hot days.        

So how do you make a horse drink? Loose salt in the feed can encourage water intake. Keeping a salt block available is okay, but some experts suggest having loose salt available since horses have a smooth tongue that doesn’t effectively lick a salt block. Some horses are clever enough to chew the edges of the salt block though. Oral electrolytes are also helpful as they pull water out of the blood and into the intestines, leading to a higher concentration of sodium (salt) in the blood.  This triggers the thirst response. Giving electrolytes approximately four hours before competition or exercise allows enough time to trigger this thirst response, encouraging the horse to drink and be well hydrated during exertion. Research during the 1996 Olympics in Atlanta found it beneficial to give daily electrolytes to horses competing under high heat and humidity. Plain water can go through the horse to the urine, so electrolytes are necessary for horses to rehydrate.        

“Ways to give oral electrolytes include paste, topdressing grain, or adding to water,” says Dr. Lydia Gray an equine veterinarian. “If electrolytes are added to the horse’s drinking water, it is important to provide a second bucket of plain water.”        

In addition to keeping an eye on the water trough, it’s important to check your horse daily for signs of dehydration. Subtle dehydration can affect performance because blood volume decreases, heart rate increases, and body temperature goes up. Knowing your individual horse’s TPR (temperature, pulse, and respiration) can be a first alert that something needs attention. Urine output decreases and becomes dark-colored, while gums become dry and pale with dehydration. One way to test for dehydration is by pinching the skin in front of the shoulder and releasing The tented skin should almost “snap” back into place. A better place to test for skin tugor (skin tent test) is the upper eyelid, though some horses may not tolerate this. When a horse’s gum above the tooth is pushed until it blanches white, it should return to moist, pink tissue within 1-2 seconds. It’s good to practice these tests when your horse is in a normal state of health so you can detect problems should they occur.        

Heat Stroke - Horses are at risk of overheating and even heat stroke when the heat index (temperature in Fahrenheit combined with the relative humidity) is above 130. So on a day when afternoon temps hit 95F and the humidity is 45% horses are at risk: 95+45=140.  When this number is greater than 150 the horse struggles to stay cool; over 180 and the horse can’t cool itself. It sounds like a big number, but when the temp is 100F and the humidity is 80% your horse is at high risk for heat exhaustion or worse, heat stroke, which is a veterinary emergency.        

According to Dr Gray, signs of a horse becoming overheated include excessive sweating or a lack of sweating, a high heart rate, a high respiratory rate - almost panting - and an elevated temperature (as high as 105-107F). Horses may also become uncoordinated and stumble, refuse to keep working, refuse to eat or drink, and may even act differently, such as becoming listless and lethargic, or irritable and cranky.        

Hyperthermia - Blood supply to muscles, the GI tract, and other organs is restricted when a horse’s body temp hits 105F. This is an emergency that requires quick action. “Stop working the horse and untack him, bringing him into the shade,” says Dr Gray. “Try to find a breeze or stand him in front of a fan, if possible. Hose the entire body with cold water. Offer cool water to drink and call your veterinarian for additional advice.”        

Anhidrosis - Some horses have a medical condition in which they don’t sweat, or sweat very little. These horses must be managed with great care to avoid overheating. In recent years several tools have shown promise. Ask your veterinary about diet, acupuncture, supplements, and appropriate housing to help your horse that has anhidrosis.        

Bottom Line - With careful daily monitoring of your equine and it’s water trough, you can help your horse/pony/donkey/mule stay hydrated through the weather challenges we face here in the mid-south.        


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