By PETER HUNTINGTON, JOE PAGAN & SCOTT O’BRIEN*
KENTUCKY EQUINE RESEARCH (AUSTRALASIA) & *RIDLEY AGRIPRODUCTS,
Summary
Electrolytes are ions (charged particles) found inside and outside of cells in the body. Electrolytes play an important role in maintaining osmotic pressure, fluid balance, and nerve and muscle activity. A horse sweats in order to get rid of excessive heat that has built up in the muscles. Horse sweat consists of water and a high concentration of electrolytes. Any level of work produces body heat and subsequent sweating. When an endurance horse sweats, it loses essential electrolytes (particularly sodium, chloride, and potassium) that are necessary for top performance. Other factors may cause a horse to sweat, such as the time the horse spends in or tied to a float during the heat of the day or the stress of an unfamiliar environment. Excessive sweating with subsequent loss of electrolytes can cause fatigue, muscular weakness and a decreased thirst response. Usually, a horse can replenish lost electrolytes from its normal diet. However, under extended work or stressful circumstances, the electrolytes that are lost in sweat cannot be replaced from the daily ration. The amount of sweat produced by an endurance horse during a competition far exceeds that of any other sport horse. It may be difficult to realize the volume of fluid lost as the sweat may evaporate before it is even seen. Because electrolyte balance is critical for maximal performance, replacement of lost electrolytes is vital. During long rides, calcium and magnesium may be also be lost in sweat in amounts high enough to cause metabolic disorders. Specific electrolyte supplementation should be provided to the horse during rides, but it may also be necessary to provide a daily dose for horses that are in training. Free choice water should always be available to the horse when electrolytes are used.
Introduction
Every endurance competitor appreciates that electrolytes are a critical component of their horse’s nutritional program. Electrolytes are mineral salts that play an important role in maintaining osmotic pressure, fluid balance, and nerve and muscle activity. During endurance exercise, sodium (Na+), potassium (K+), and chloride (Cl-) are lost in large quantities through sweating. Loss of these electrolytes causes fatigue and muscle weakness, and decreases the thirst response to dehydration. It is vitally important that endurance horses begin competition with optimal levels of fluids and electrolytes in their bodies, and that these important nutrients are replaced throughout a ride. This article will discuss the electrolyte requirements of endurance horses during training and competition and present strategies for electrolyte supplementation during a ride.
Sweat Losses
It is important to have some idea of the magnitude of electrolyte loss a horse incurs during exercise before a feeding program can be developed to replace these losses. Because most electrolyte losses in the horse occur through sweating, one method of calculating electrolyte requirements can be based on different amounts of sweat loss. Table 1 contains the levels of key electrolytes required per day by a horse at rest and after exercising.
TABLE 1. Total daily electrolyte requirements (g/day) as a function of sweat loss.
Sweat loss (litres/day)
Electrolyte Rest 5 litres 10 litres 20 litres 40 litres
Sodium (Na+) 15-20 33 50 85 155
Chloride (Cl-) 27-33 55 83 139 251
Potassium (K+) 40-50 46 52 64 88
The amount of sweat loss will depend on a number of factors such as duration and intensity of exercise, temperature, and humidity. In general, horses exercising at low intensity (12-18 km/hr) will lose between 4 and 10 litres (L) of sweat per hour. During higher intensity exercise (30-35 km/hr), sweat loss levels reach as high as 15 L per hour.
Electrolyte Requirements during Training
Daily electrolyte requirements can be estimated by calculating the total amount of mileage logged weekly by the horse, taking into account the environmental conditions under which the training occurs (Table 2). For example, if an endurance horse were logging 50 km of work per week in a cool environment (20-25oC), it would only require about 60-120 g of a well-formulated electrolyte supplement to meet its daily electrolyte requirements. The lower range of supplementation would be adequate if the horse was also receiving adequate forage and a grain mix that contained supplemental salt, as well as access to a salt block. Some bore water sources can also contribute to electrolyte intake. Horses at rest will normally consume around 40 - 60 g of salt per day from a salt lick or loose salt. As mileage and environmental temperature increases, so does the requirement for electrolyte supplementation. Horses that are training heavily in a hotter environment may need 140-200 g of supplemental electrolytes daily.
Table 2. Total daily electrolyte requirements (g/day) as a function of training intensity and environment
Weekly mileage and training environment
Electrolyte 50 km/wk
(temperate1 50 km/wk
(hot2) 75 km/wk
(temperate) 75 km/wk
(hot) 100 km/wk
(temperate) 100 km/wk
(hot)
Sodium (Na+) 24 32 27 40 32 48
Chloride (Cl-) 40 54 47 67 54 80
Potassium (K+) 43 46 44 49 46 51
Daily electrolyte supplementation3 30 - 90g
60-100 g
45-90 g
75-120 g
60-100 g
90-150 g
1 Temperate = 20-25oC
2 Hot = 33-35oC
3Based on the composition of Equivit Restore and consumption of 30 - 60g of salt. The amount of daily electrolyte supplementation will depend on the amount of electrolyte already in the ration from other sources and whether the horse has access to a salt block. If horses are trained in temperatures less than 20 degrees needs will reduce
The recommendations given above are based on supplementing electrolytes at the same rate daily even though the amount of exercise performed each day will vary. This is probably a reasonable approach to supplementation except for days when the training distance is especially long. For those days, additional supplementation may be warranted. As a rule of thumb, 60 g of electrolyte supplementation are required for each hour of exercise in moderate climates. This rate of supplementation will double in hot environments when sweat loss is extensive. A long training ride of 60 km (~4 hours) in moderate temperatures would therefore produce enough sweat loss to require 240 g of electrolyte supplementation. This level of supplementation could need to be partially provided during the ride (60 g at 20 and 40 km) using an oral electrolyte paste with the remainder of the electrolyte administered after the ride. If the horse will not consume this quantity of electrolyte in a single meal, then 60 g can be administered as a paste at the end of the ride. When administering oral electrolyte pastes, it is absolutely essential that the horse have access to drinking water. If the horse refuses to drink, do not administer an electrolyte paste.
Supplementation During Competition
There is a great deal of controversy about how to administer electrolytes during competition. A number of different strategies have been used successfully by competitors, and the recommendations that will be given here are not necessarily the only way to achieve success.
During competition, sweat losses can be very large. How much water and electrolytes does an endurance horse lose during a competitive ride? Using the sweating rates described earlier, an endurance horse will lose between 45 and 60 L of sweat during a 160 km ride. This represents electrolyte losses of 460-690 g. Additionally, 9-14 g of calcium and 5-8 g of magnesium will be lost through sweating. It is debatable whether all of these losses can or need to be completely replaced during the competition. Research has shown that endurance horses participating in 80-160 km events often have a fluid deficit of 20 to 40 L despite having access to water and electrolytes during the ride. Canadian researchers have shown, however, that endurance horses with less pronounced fluid and electrolyte alterations during a competitive ride were more successful than those with greater changes. Therefore, it is absolutely essential that a large proportion of the electrolytes and water lost in sweat be replaced during the ride.
Pre-ride electrolyte loading
The endurance horse must start the competition with adequate stores of both water and electrolytes. This can be accomplished in two ways. Firstly, the horse should be on a high level of forage (hay or pasture) intake before a ride. When a horse is fed liberal quantities of forage, it can store extra water and electrolytes in its large intestine. These stores can be called on to replace sweat losses early in the ride. Second, extra electrolytes can be administered the night before and the morning of the ride. The horse’s system is finely tuned to balance the amount of electrolytes and water that it stores in its body at rest, so excessive pre-ride electrolyte supplementation should be avoided. Moderate supplementation (30 - 60 g the night before and 30 -60 g the morning of competition) will ensure that the horse has adequate electrolytes within its body and will provide additional electrolyte stores within the gastrointestinal tract.
Electrolyte supplementation during competition
Electrolytes should be supplemented throughout competition. The type of electrolyte supplement used during competition is slightly different than that which is used during training. This electrolyte should provide additional calcium and magnesium along with sodium, potassium, and chloride. If calcium and magnesium losses are not replaced by mobilization of skeletal stores or by supplementation, metabolic disturbances such as thumps may occur. Electrolytes should be administered to horses at each vet check and can also be given at water stops along the trail. The best way to administer electrolytes is in the form of a paste. Pastes are commercially available, or they can be made up fresh at the vet check by diluting an electrolyte powder in applesauce, water, or liquid antacid. A reasonable dose of electrolyte powder (or equivalent) is 30 - 60 g at each vet check. Thirty to 60g doses of electrolyte can be administered on the trail. It is worth reemphasizing that the horse must have access to drinking water when receiving concentrated electrolyte pastes. These pastes are hypertonic (a greater concentration of electrolytes) compared to blood and will effectively draw fluid out of the horse into the gut if they are not diluted by drinking water.
Administering large doses of electrolytes without adequate water intake will result in serious problems, including colic, dehydration, and possibly death. To ensure water intake at rides, many riders train their horses to drink molasses in water and this can disguise taste variations, plus it adds a little energy and potassium. Adding small amounts of powdered soluble electrolytes to water can aid replacement, but too much can lead to reduced water intake which is counter productive. Most commercial liquid electrolytes don’t provide enough electrolytes to be of real value to the horse and you need to use powdered forms or pastes to get enough electrolytes back into the horse.
If you are feeding a commercial feed at vet checks it will contain some electrolytes that will contribute to replacement and most people feed a wet feed at vet checks so that will get water in as well. Hay and molasses in water will help replace potassium losses. If you are mixing your own feed at vet checks, be careful not to overload it with extra electrolytes as this can reduce intakes. If the feed is more than 2.5% salt, palatability can decline so you may only get 1 scoop (30g) of electrolytes safely into the feed at a ride. At home, when meals are larger and the horse has more time to eat, you may be able to get 2 scoops into the horse in a post ride – meal.
Post-ride supplementation
Administering 120-240 g of electrolyte over the 24-hour post-ride period can eliminate most of the post-ride electrolyte deficit. A portion of this can be given as a paste shortly after the conclusion of the ride followed by top-dressing supplementation of electrolyte on the next two or three meals.
Choosing a Product
There are a heap of commercial electrolytes on the market and plenty of home recipes, so how do you know what to use? All horses should have access to a salt block or rock salt during training. Endurance horses don’t need alkaline electrolytes so avoid products aimed specifically at racehorses that contain bicarb or citrates. You want a strong electrolyte with plenty of sodium and chloride and only small quantities of fillers such as glucose. Glucose may improve palatability, but doesn’t help replace what is lost in sweat. Vitamins may be useful, but aren’t really important in this context. There are some products specifically formulated for use in endurance horses during the ride and these are worth considering. They usually contain extra calcium and magnesium. Commercial pastes are available or you can mix up pastes using a powdered electrolyte and applesauce. These can be done at home and then taken to the ride.
Conclusion
The health and well-being of the endurance horse can be enhanced by proper electrolyte supplementation during training and competition. The level of supplementation should be adjusted to match sweat losses, which are affected by exercise intensity, terrain, and environmental conditions. A well-formulated electrolyte supplement should be used during training that replaces the quantities of sodium, potassium, and chloride lost in sweat. During competition, an electrolyte that also contains calcium and magnesium should be used to prevent metabolic disturbances such as thumps from occurring. Electrolytes should only be administered when the horse has access to water because both electrolytes and water are needed to maintain optimal fluid balance.
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