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How important are electrolytes in my horse’s diet?

know your horses vital signsHorses depend on certain electrically charged minerals to maintain the balance and flow of vital body fluids, the transmission of nerve impulses, and the healthy function of the muscles and the circulatory system. These minerals are called electrolytes. Their positive and negative charges help to control the body’s pH (acid/base) balance and the transport of nutrients and waste products in and out of the cell.

The minerals sodium, potassium, chloride, calcium, and magnesium collectively are termed electrolytes. When dissolved in body water, those minerals are electrically charged particles called ions. Sodium and chloride are the primary electrolytes contained in blood plasma and extracellular fluid, while potassium is the chief intracellular electrolyte. These electrolytes are critical for a large number of body functions. For example, electrolytes modulate fluid exchange between the body’s fluid compartments and regulate acid-base balance. Sodium and potassium are important for the establishment of proper electrical gradients across cell membranes. Calcium and magnesium also are important in this regard. These electrical gradients are vital for normal nerve and muscle function–electrolyte deficiencies or imbalances therefore can impair nerve and muscle function. The kidneys are of prime importance in maintaining electrolyte balance. Some electrolytes are lost in manure, but most of the fine-tuning is done by the kidneys. In general, sodium is highly conserved – very little is excreted in the urine. On the other hand, the kidneys excrete substantial quantities of potassium and calcium on a daily basis. This is partly due to the fact that dietary intake of potassium and calcium tends to be high.

Remembering that horses are around 60% waters, that works out to be around 270 kg of water from an average 450 kg horse. This is why electrolytes are so important in the horse.


What do each electrolytes do?

Following are some of the functions that each of the main and a few lesser known electrolytes do in the bodies function.


Sodium and Chloride

NaCl, common salt, is the major electrolyte of the body. Salt is comprised of two electrolyte ions (charged particles) – sodium (Na+) and Chloride (Cl-). It is found in much higher concentration outside the cells (in the blood and other fluids surrounding the cells) than in the cell themselves.

The saltiness of the blood is measured as it is filtered through the kidneys. This way the body knows how much water to release in the urine to keep the concentration of salt in the blood at normal levels.

The saltiness of blood can also influence sweating. When the horse becomes dehydrated and the blood sodium level is much more concentrated, sweating will slow or even stop as the body is trying to preserve the critical balance of salt to water. However, without adequate sweating, dangerous overheating can result.



Inside the cells, potassium (K+) assumes the role as the major positively charged electrolyte. One of potassium’s major roles is to keep the sensitivity of nerves and muscles at normal levels, not under or over reactive to impulses telling them to contract. This includes both skeletal and heart muscles.

Even relatively small changes in total potassium can negatively affect athletic performance. Because the sensitivity of the nerves and muscles is based upon maintaining a fairly constant gradient between the potassium and sodium outside the cells, the body works hard to keep the bodies potassium level within a narrow normal range. To do this, the blood sometimes ‘robs’ potassium from the inside of cells. Consequently a blood test is not always a reliable method of picking up problems with potassium because it only indicates the amount of potassium circulating in the blood. It doesn’t tell about potassium within the cells. But, if blood levels are low, you can be sure that the levels inside the cells are in even worse shape.



When we hear of calcium, we think of bones and teeth. This is indeed a major function of calcium in the body, and most of the calcium is found within bones and teeth. However calcium in its ionic form (Ca++) is an important electrolyte. Like potassium and magnesium, it is critical to the normal function of muscles and nerve tissue. Also like potassium, the levels of calcium in the blood are closely regulated by the body to be kept in a narrow normal range. If need be the body can “rob” itself from the bones and other body cells to maintain its calcium blood levels.



Magnesium is probably the most overlooked electrolyte. Although found in much smaller amounts than many other electrolytes. It has a critical role to play. Magnesium functions as a co factor for over 300 enzyme reactions within the body. This means if magnesium is not present or is present in an insufficient amount, each of these 300 reactions will suffer.

Magnesium is the critical CO factor for reactions that involve the burning of glucose in the presence of oxygen. (The most important power source for all aerobic exercise). Magnesium is involved in the metabolism of fats and proteins as well. It is also essential for DNA to be able to send messages to the cells. Magnesium is an essential link in the chain of command from the “brain” of the cell, the nucleus to the other structures within a cell. Magnesium is required for normal muscle function, especially for relaxation of a muscle.



Phosphorous is involved in the formation of bone. About 85% of the body’s phosphorous is located inside the bones in a solid form. The remainder is distributed between the blood and the interior of the cells. Inside cell, phosphorous is absolutely essential to the normal metabolism of carbohydrates, fats and proteins, as well as the generation and storage of energy from basic fuels.



Manganese is a mineral/electrolyte you rarely hear about. Like magnesium, manganese is present in relatively tiny amounts compared to many other electrolytes, but it is essential to the formation of normal connective tissues (tissues that hold your body together), and the formation of joint cartilage. Manganese plays a role in the metabolism of fat, the creation of DNA and the manufacture of cholesterol. (A certain amount of cholesterol is needed to form the backbone of many of the body’s most important hormones. Because the cholesterol in food is broken don before it is absorbed, the body has to make its own cholesterol.)



Copper is also present in basically very small amounts compared to the major electrolytes. The utilisation of iron to make red blood cells requires copper. Formation of the protective outer coating on nerves also requires copper, as does the production of skin pigments and the formation of healthy collagen – the major component of tendons and ligaments. Similarly, healthy joint cartilage can only be produced when there is adequate copper available.


Cation Anion Balance

During the intensive work of training and performance, the production of energy from food fuels releases increasing amounts of acid by-products. The best known of these is lactic acid, or lactate. As these acids accumulate in the muscles and the blood, the body’s pH drops, metabolic efficiency declines and the stage is set for fatigue and reduced performance. Proper nutrition offers several avenues for controlling this problem and maintaining the body’s pH within the optimum range for a longer period of time. Electrolytes play a major role in the body’s efforts to buffer excess acidity. Positively charged mineral ions (Na+, K+), called cations, improve the processing of the large amounts of hydrogen ions released during exercise metabolism, and thus maintain better pH. When excess negatively charged minerals, or anions, are present, acidity increases and performance suffers. Studies show that a more positive dietary cation/anion balance (DCAB) can be an important part of the successful control of exercise-induced acidity.


Fluid Losses

Exercise generates a great deal of heat that must either be dissipated from the body or stored. The dissipation of heat is very important, because if a large amount of heat is stored, body temperature will rise to dangerous levels. In the horse, the processes that contribute to the dissipation of heat during exercise include radiation, convection, conduction and evaporation. Of these, evaporation may be the most important; particularly when horses are exercised in warm conditions. To facilitate evaporative cooling, horses sweat. Sweating is certainly desirable as a means to maintain body temperature, but high sweating rates result in high rates of water and electrolyte loss.

In a practical setting, it is difficult to accurately measure the total amount of sweat that a horse loses during an exercise bout. However an estimate of sweat losses can be obtained by weighing horses before exercise and after exercise.

Recently there has been some research involved in weighing horses before and after workouts, races or other events to estimate sweat losses. At this time they have not weighed enough horses in different environmental conditions to have solid estimates of sweat losses in all situations but some examples of weight losses that have been observed in field conditions are shown below.

Range of weight losses when horses were weighed before and after various events**

Type of horse
Range of weight loss (kg)
Standard Harness Horse
(before and after a 1 mile race)
5 to 15
Field Hunters
(before and after 3 hours of fox hunting)
10 to 45
Thoroughbred horses in race training
(before and after galloping)
4.5 to 7
Endurance horses
(from the night before a race to the end of 85km)
10 to 40

** These values may not apply to all horses performing these types of events

Almost without exception, the owners, trainers or riders/drivers of the horses are amazed at the weight differences of their horses before and after work. Although there are often faecal losses during exercise, weight loss during most types of exercise is generally thought to be about 90% water, so clearly water losses during some activities are quite large.

Where does the water in sweat come from? The horse’s body is about 65% water. Most of the water is contained in cells (intracellular water) but some is outside of individual cells (extracellular water). Blood plasma, which constitutes a large portion of the horse’s blood volume, is an important component of the extracellular water pool. When horses (or humans) sweat, some of the water in sweat is obtained from the plasma volume. Consequently, if sweat losses are large, the plasma volume may decrease. A reduction in plasma volume (and thus total blood volume) may affect the ability of the horse to maintain adequate blood flow to muscles during work. Progressive dehydration may also result in a reduction in sweating rate and thus an increase in body temperature.


Electrolyte Losses

Horse sweat contains many things besides water. Horse sweat contains calcium, magnesium, some trace minerals and protein. However, most notably, equine sweat is relatively high in sodium, chloride and potassium. When horses lose large volumes of sweat, they lose considerable quantities of these electrolytes. Although we have not measured the amount of electrolytes actually lost during various events, it is possible to roughly estimate electrolyte losses if the approximate sodium, potassium and chloride content of sweat is known. Many researchers have measured the amount of the various electrolytes in sweat. Chloride is present in the highest concentration, but sodium and potassium concentrations are also reasonably high. The following table provides estimates of the sodium, chloride, and potassium losses that might be experienced by horses in various activities, given the weight losses listed earlier.

Range of Estimated Electrolyte Losses of Horses Performing Different Activities**

Type of horse
Sodium (g)
Potassium (g)
Chloride (g)
Standardbred – (during a race)
16 – 46
6 – 17
31 – 88
Field hunters – (3 hour foxhunt)
33 – 148
12 – 51
63 – 284
Thoroughbred – (during a workout)
16 – 23
6 – 8
31 – 44
Endurance horse – (85km ride)
33 – 132
12 – 48
63 – 252

** These values are estimated from weight loss during exercise and approximate composition of equine sweat. Many factors could cause the actual values for a particular horse to be higher or lower.

It is apparent that heavily sweating horses experience large electrolyte losses as well as large fluid losses. Electrolytes have many functions including maintenance of acid-base balance in the body fluids and nerve and muscle function. Large losses of electrolytes can result in several neuromuscular and systemic disturbances including muscle cramping, tying up, synchronous diaphragmatic flutter (thumps) and systemic alkalosis. Horses with large electrolyte losses may also have reduced sweating rates and therefore a reduced ability to manage body temperature. Electrolyte concentrations in the blood may play a role in the horse’s thirst response or desire to drink. Ironically, when horses sweat a lot and lose a considerable amount of sodium, their thirst response may be depressed and the horse will not drink adequate fluids to maintain a desirable state of hydration.


Electrolyte Supplements

There is a plethora of electrolyte supplements on the market. Generally if a horse is eating a balanced diet and is not experiencing extreme electrolyte losses (heavy sweating, intense exercise, humid tropical conditions or disease), the benefit of these supplements is questionable. If you expect heavy electrolyte losses, a supplement can be beneficial, but it is important to remember that the electrolytes are not stored in the body, so if they are administered when the electrolytes are in balance, the body most likely will view them as an excess, and the kidneys will get rid of them. It is important to give electrolytes while the loss is occurring (during long endurance rides, for example) or shortly after to replenish the loss.

Encouraging water consumption is extremely important. This often starts by making sure your horses have free access to a good, clean water source. For horses which travel extensively, it actually might be necessary to bring water from home; this can help keep them drinking on the van and get them started in a new location. Many people have had good success using various flavours of cordials or molasses to mask the foreign taste/smell of a new water source.

In the winter months, there is no question that offering room-temperature water (from the house, not the cold tack room) during the cold can increase a horse’s daily water intake by as much as 100%. Keeping a horse’s water intake normal during the winter months might help reduce the incidence of impaction type colic.

Hygain Regain Horse Feed SupplementMany electrolyte products are commercially available and recipes for home made mixes can be found in textbooks or magazine articles. The most appropriate way to choose a product is to compare the electrolyte content of the supplement to the electrolyte content of sweat such as HYGAIN REGAIN. If economy is a concern, the supplement should be evaluated on the basis of $/units of actual electrolytes, not $/unit of supplement, since many supplements may contain a lot of “filler” ingredients such as sugar. Some “electrolyte” supplements actually contain very low levels of electrolytes, or are designed. For horses that have electrolyte disturbances from disease, rather than exercise.


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