Electrolyte supplementation in the exercising horse

Proper hydration is a non-negotiable in the performance horse.  Maintain hydration by replacing electrolytes lost during exercise, competition and transport with Performance XL: Electrolyte from Mad Barn.

A discussion about electrolyte supplementation is really about thermoregulation and being able to dissipate heat. The horse demonstrates what is likely the highest sweat rate within the animal kingdom and uses this to dissipate ~70% of the heat produced during exercise. It shouldn’t be surprising that such high sweat rates, which can approach 20 L per hour, are required when you consider the tremendous oxidative capacity and range of the equine athlete. For example, the volume of oxygen consumed per kilogram of body mass in the human increases about 2 fold when comparing rest to high intensity exercise. In the horse there is a 35-fold increase in oxygen consumption. The tremendous oxidative capacity of the equine athlete allows it to perform a tremendous amount of work at relatively high speeds, which in turn generates a lot of heat which must be dissipated and the majority of this is done through sweating.

Evaporative cooling through sweat is accompanied by a substantial loss of electrolytes. Unique to the equine, is sweat that is isotonic or slightly hypertonic, unlike the human athlete which has hypotonic sweat. Therefore, during intense exercise or prolonged moderate intensity exercise, there is a substantial loss of electrolytes.

The rate of sweating and electrolyte loss is directly proportional to the level of work performed and the ambient temperature and humidity. Level of conditioning and acclimatization also impacts the rate of sweating and electrolyte loss. Based on sweat composition studies, sodium losses through sweat are approximately 4 g per liter of sweat lost. Therefore, a horse sweating at a rate of 10 L/hr performing an hour of work, total sodium loss would approach 40 grams. Which is equivalent to 100 grams of salt (sodium chloride).

Any electrolyte supplementation program has to be taken in the context of the whole nutrition and conditioning program. It should be the goal of your nutrition program to provide at least 125% of the required electrolytes in the daily diet, please note this does not need to be done through commercial electrolyte supplements. This can be achieved through readily available feed ingredients.electrolyte

For example, a horse undergoing intense exercise, as defined by the NRC as 6-12 hours of slow work and 1 hour of speed work per week, the electrolyte requirements are: Na, 41g; K, 53 g; Ca, 40 g; Mg, 15 g; Cl, 93 g. An average quality hay will meet all these requirements if fed in sufficient quantities, with the exception of sodium and chloride. Therefore, in a balanced diet, the only requirement to meet electrolyte needs is the addition of salt. At this level of work, that would require approximately 125 grams of salt per day – equivalent to roughly half a cup. Please note that the entire nutrition program is more complicated than this, but is outside the scope of this article. Please seek the advice of a qualified nutritionist for balancing your equine athletes diet.

Having the diet properly balanced for electrolytes is important, but does not exclude the use of homemade or commercially prepared electrolyte solutions to be used during a competitive event or intense training day. Lindinger and Ecker (2013) demonstrated that a well formulated electrolyte supplement given prior to exercise increased the time to voluntary fatigue by 33%. Many other studies and experience have shown improvements in performance by providing electrolyte solutions prior, during and following strenuous bouts of exercise. In the case of electrolytes, an ounce of prevention is worth a pound of cure.

Given the myriad of electrolyte supplements on the market and the vast difference in requirements for horses in various disciplines, it is impossible to provide a standard set of guidelines for supplementation practices. In general, supplementation should begin prior the event, frequently during the event (30 min intervals) and continued well into the recovery phase. Depending on the event and level of exercise a substantial amount of the sweat loss will actually occur after the bout of exercise. It is imperative that electrolyte supplementation be continued through the recovery phase.

The great sugar debate!

There is a lot of rhetoric in the commercial marketspace about electrolytes containing sugar and even in academia as to the level of sugar (glucose) that is appropriate. When confronted with this, my response is usually as such: “If the horse is working hard enough to require electrolyte supplementation, then the electrolyte should contain sugar.” There are many benefits of sugar administrated with electrolytes: 1) promotes the uptake of sodium from the gut, 1) enhances cellular potassium absorption, 3) stimulates the rate and completeness of rehydration, and 4) provides a ready source or energy and may enhance glycogen synthesis in recovery. The literature consistently indicates that the inclusion of glucose in electrolyte solutions enhances performance.

The hypothesized downside of providing sugar with the electrolytes is the concomitant increase in blood glucose and insulin and the proposed ‘sugar crash’ that would occur after, therefore decreasing performance. The literature simply does not support the ‘sugar crash’ phenomenon. As already stated, the literature consistently shows improvements in performance when sugar is a component of the electrolyte solution.

Many authors also state that sugar should not be the first ingredient in a properly formulated electrolyte. Again, this is misleading, as a good number of studies showing improved performance with electrolyte supplementation, glucose was in fact the most abundant ingredient. This means it would be the first ingredient if regulations require the ingredients to be listed in order of abundance. Regulations in Canada do require that the order of ingredients be listed in order of abundance from greatest to least. This is not the case in the US where regulation is at the state level. Some states do not require ingredients to listed in order of abundance. Therefore, depending on where the product is manufactured, the order of ingredients may have no relevance to the abundance of that ingredient in the product.

In summary, a properly formulated electrolyte should contain some glucose and the electrolytes should be balanced to replace what is lost in sweat. Electrolyte administration should begin prior to the event, during the event and the recovery phase. Administration should be frequent and before any signs of dehydration are evident.   Most importantly, there should be a source of clean fresh water (no electrolytes added) available at all times.


1. Electrolyte – a substance that produces an electrically conducting solution when dissolved in water

2. Cation – positively charged electrolyte:

  • Sodium (Na+)
  • Potassium (K+)
  • Magnesium (Mg++)
  • Calcium (Ca++)

3. Anions – negatively charged electrolyte:

  • Chloride (Cl-)
  • Phosphate (HPO4-)
  • Bicarbonate (HCO3-)

4. Intracellular – inside the cell

5. Extracellular – outside the cell

6. Solute – general term to describe the ions in a solution. In a mixture of water and electrolytes, the electrolytes are considered the solute.

7. Tonicity — the relative concentration of solutions that determine the direction and extent of diffusion

8. Hypotonic – used to describe a solution with less solute per unit of water than the one it is being compared to.

9. Isotonic — used to describe a solution with the same amount solute per unit of water than the one it is being compared to.

10. Hypertonic — used to describe a solution with more solute per unit of water than the one it is being compared to.

11. Salt – most often used to describe table salt/sodium chloride. In chemistry through a salt is an ionic compound that results from the neutralization reaction of an acid and a base. The distinction is important as in some literature, salt is often referred to and is not strictly relating to sodium chloride.

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