If you’ve been keeping a close eye on the latest Gatorade TV advertisements, you’re acutely aware that without the proper hydration strategies during a tough workout, you can be reduced to a desiccated pile of human rubble on the treadmill or left to drag your twitching body on all fours toward the finish line of the Ironman competition.

While most of us don’t push ourselves to quite the extremes depicted on these TV spots, we could be riding our horses into trouble if we aren’t careful to keep them hydrated and supplied with adequate electrolytes, particularly as the weather grows more hot and humid.

Evaporation of sweat accounts for approximately 65 percent of a horse’s heat dissipation, and an exercising horse produces quite a bit of heat.

“A horse racing at 13 meters per second [that’s about 28 miles per hour] produces enough heat to bring 8 liters of water from room temperature to a boil. That’s enough heat to bring more than 2 gallons [1 gallon equals about 4 liters] of water to a boil after just a two-minute race,” wrote endurance veterinarian Kerry Ridgway in On To Atlanta ’96, a publication prepared as part of the research for the anticipated stressful weather conditions of the 1996 Olympic Games in Atlanta.

“Even more astounding, an endurance horse traveling at about 17 km/hr sweats approximately 12.5 liters every hour and produces enough heat in that hour to bring about 25 gallons of water from room temperature to a boil.”

That’s a lot of heat to sweat away. To complicate matters, the horse has a low surface area to weight ratio–one-third that of your typical human–meaning they don’t have a lot of skin from which they can evaporate all the heat produced by their massive bodies. In order to compensate, they can produce 10 to 15 liters of sweat per hour.

“Losses of up to 18 liters were observed in a three-day event horse simulated cross-country day exercise test. This figure was very similar to the actual losses at Atlanta in the leading eventers,” reported a study by Kentucky Equine Research Inc., the official equine nutritionist of the U.S. Equestrian Federation. “Sweat losses of up to 25 liters a day may occur in a horse that sweats heavily during travel to a competition or prior to an event whilst waiting for the big moment, and that horse then faces the added losses of an event itself.”

System Depletion

The problem with horses being such big, sweaty beasts is that in addition to the huge volumes of water being lost, they’re also losing surprisingly large amounts of electrolytes.

Electrolytes are salts that separate into positively and negatively charged ions when dissolved in water. The most prevalent ones are sodium (Na+), chloride (Cl-), potassium (K+), calcium (Ca2+) and magnesium (Mg2+). Sodium and chloride, which join forces to become table salt (NaCl), comprise approximately 80 percent of the electrolytes found in sweat. It’s no wonder sweat tastes so salty!

Electrolytes are found throughout the body, inside and outside of every cell, and give each cell an electrical charge based upon their concentrations. As a result, they’re an integral part of virtually every physiological function in the body, including muscle contraction and transmission of nerve impulses.

Disturbances in electrolyte concentration can therefore cause a host of maladies, such as heart problems, colic, tying up and thumps.

The sweat glands of a well-conditioned human adapt to conserve the electrolytes excreted from the body, but horses show little ability to regulate the amount lost, regardless of their fitness level. This mass electrolyte exodus makes a horse’s sweat hypertonic in comparison to its blood plasma, which means the sweat contains a higher concentration of electrolytes than the plasma. So, when a horse sweats, its plasma loses electrolytes at a faster rate than it loses water and becomes progressively less “salty.”

The situation becomes further compli-cated by the mechanisms that control whether or not your horse feels thirsty. A horse gets the thirst signal if he experiences a drop in blood volume, which means he’s already quite dehydrated, or if the sodium concentration in the blood increases. That unfortunate fact means that the horse who has been sweating away gallons of electrolyte-rich water isn’t going to feel thirsty until he’s so dehydrated that his blood actually thickens.

Warped though it may sound, it makes sense–since electrolytes are so important to so many systems, when the levels are low, the body isn’t going to seek out more water to dilute what it has.

Dehydration is measured in percentage of body weight lost by the horse. Losses of 5 percent or less can be clinically difficult to detect and are generally well tolerated, but such levels can already adversely affect a horse’s performance.

Worsening dehydration can be identified through various indicators, including: capillary refill time (CRT) in the gums of more than two seconds; slow refill of the jugular vein; scarce and/or dark urine; reduced skin elasticity (the “skin tenting” pinch test); and dry mucous membranes and feces.

When dehydration reaches critical levels, sweating ceases in the body’s attempt to retain enough fluid to maintain kidney function and blood volume. If the horse is still hot at this point, its respiration rate will increase to the point of panting in the body’s effort to cool itself by dissipating heat through the lungs and blood vessels lining the nasal cavity.

As dehydration increases, the pulse also elevates, as the heart has to pump faster to circulate the smaller volume of blood around the body. It becomes difficult for the thicker blood to penetrate into capillaries, which, in conjunction with other factors, contributes to incidences of laminitis, tying up and colic.

Respiration and heart rates obviously also increase with exercise, but if they don’t return to normal levels with proper cooling-out techniques, it’s a sign your horse is dehydrated.

Drink Up

Electrolyte supplementation is a vital component of the health and well-being of horses under unusual stress, particularly during hot, humid weather, which retards the cooling effects of sweat evaporation. Their use not only replenishes the salts required for the horse’s systems to function properly, but also encourages the horse to stay hydrated by stimulating its thirst response.

Hal Schott, DVM, Ph.D., of Michigan State University’s College of Veterinary Medicine, has worked with a team of researchers over the course of several years to discover ways to encourage voluntary hydration in horses. They studied various hydration strategies on horses performing simulated 36-mile endurance rides on a treadmill.

“When the horses ran without electrolyte supplementation, they lost about 50 pounds of fluid as sweat and replaced about half of this loss by drinking about 3 gallons (nearly 25 pounds) of water,” said Schott in an article about his team’s work. “However, when they ran with electrolyte supplementation [salts were given as a slurry dosed into the mouth before and during the run] the horses drank between 5 and 6 gallons (40 to 50 pounds of water), replacing nearly all of the fluid lost in sweat.”

In addition to drinking more water, the horses also began drinking earlier in the course of the endurance test.

“Adding electrolytes to the endurance horse’s competitive life is absolutely essential, with the exception of a very few rarities that say that don’t use them,” said Jeannie Waldron, DVM, an endurance rider and veterinarian at the Rectortown Equine Center in Virginia. “To make a safe sport of it and allow the horses to do their best, you cannot avoid using electrolytes.”

With a host of electrolyte powders, pastes, gels and cookies lining your tack shop or feed store’s shelves, it’s important to read the
labels because not all electrolyte products are created equal.

Waldron recommends avoiding those with sugar, dextrose or corn syrup listed as the first ingredient because they’re not electrolyte-dense and it’ll take a lot more of the product to get the dose you’re after. Look for combinations of easily absorbable salts, such as sodium chloride/calcium chloride or calcium acetate/potassium chloride. Avoid di-calcium phosphate, which is cheap but not absorbed well, and bicarbonate formulations, which are geared toward horses with diarrhea.

Waldron doesn’t recommend giving horses a daily ration of electrolytes, beyond free-choice salt, unless you’re anticipating a possibly stressful activity. Most horses, beyond those in heavy exercise, get all the electrolytes they need from good-quality hay and from salt added to commercial feed mixes. Horses can’t store surplus electrolytes, so any extra they consume are eliminated and wind up being shoveled into the muck bucket.

An inexpensive (though not as easily absorbed) alternative to commercial electrolyte preparations is a home blend of three parts table salt (NaCl) to one part “lite” salt (KCl).

Electrolyte powders can be mixed with whatever medium your horse likes–applesauce, yogurt, molasses (Waldron’s preferred method)–and dosed directly into the mouth with a reusable blunt-tip syringe. They can also be mixed directly with feed, but many horses won’t eat them this way, and the electrolytes won’t do your horse any good at the bottom of his feed tub. Adding electrolytes to water is generally not recommended–you can’t control how much your horse gets–but if you do, it’s vital that you also provide access to plain water.

Supplementation before a long trailer ride or bout of exertion can begin the night before, to help ensure the horse is well-hydrated to start. A general recommendation for dosage size is 2 oz. of electrolytes, but consult with your veterinarian and consider the specific conditions your horse will be facing the next day and adjust accordingly.

Another dose can be given an hour or two before the activity the next morning and another after the work or stress is completed. If the horse’s exertion is going to be prolonged, such as during a long haul in the trailer or an endurance ride, give further doses every three hours or so and let the horse drink freely at every opportunity.

Allow your horse to drink before giving him electrolytes as some horses are put off from eating and drinking immediately after receiving a concentrated dose.

Schott and his team explored other methods of stimulating voluntary hydration in other studies of horses performing simulated endurance rides. During the first five minutes after the exercise, the horses were offered either plain water or 0.45 percent or 0.9 percent salt water. The horses’ consumption of plain water over the next hour was then monitored.

“We found that an initial drink of salt water improved recovery of sweat fluid losses, because horses drank more water when it was offered a few minutes later. In contrast, horses that were offered plain water for their initial drink did not drink further during the initial hour of recovery despite the fact that they remained partially dehydrated,” reported Schott.

Another study run by his team compared consumption rates for water at different temperatures. The horses showed a preference for ambient temperature water (like it comes out of the hose) versus that which was warmed or cooled.

Schott’s team also further debunked what has essentially become a rural legend that you shouldn’t give horses water immediately after exercise. While restricting their initial access to water didn’t adversely affect their test subjects’ total water consumption during the hour following exercise, the team observed no negative effects of allowing unlimited access. So if your horse is hot and wants to drink, let him.

Fluid Replacement Therapy

Sometimes, despite our best efforts to prevent it, a metabolic problem can arise as a result of dehydration or electrolyte depletion. When a horse fails to progressively recover following exercise or when its condition worsens at rest, fluid replacement therapy may be required. Fluids can be administered orally via a nasal gastric tube or intravenously.

Some competitors will use fluid replacement therapy as a preventative measure to pre-load their horses with fluids before competition. This practice can be used to hydrate horses already showing signs of dehydration or to eliminate the 3 to 5 percent dehydration that can be difficult to detect but that can affect performance. A horse can only hold so much–they can’t be supersaturated with fluids–and any excess will be urinated away.

Fluid replacement therapy should be viewed as a medication and not performed as a routine procedure, regardless of whether or not the horse required the assistance. Consult with your veterinarian and take into account the specific weather and stress conditions of that day and the condition of your horse to determine whether or not fluid replacement is advised.