Understanding Electrolytes in Horses

How your horse uses and loses electrolytes is important, especially for long-distance competition horses.
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endurance horses at sunrise

Research done on distance riding events reveals that the greatest loss of fluids and electrolytes occurs within the first 20 miles.

The food your horse eats is converted into energy fuel to drive locomotion. Approximately 70-80 % of this energy conversion is wasted as heat, which is dissipated from the inner recesses of the horse’s body as sweat. Horses sweat three times as much as a human per a given surface area of skin. While a person might shed two liters of sweat in an hour, a horse might evaporate or drip away 15 liters in that same hour.

Where Do the Electrolytes Go?

Horse sweat is hypertonic, meaning lots of salt is lost in sweat. You can see this as you brush your horse’s dry coat after a good workout. In contrast, human sweat is hypotonic, meaning there is more water in it than salt. There are several factors that influence how much electrolytes are lost when your horse exercises. Longer bouts of activity, a hot and humid climate or an unfit horse can all contribute to higher electrolyte loss.

Review of Neuromuscular Function

The interaction of nerves and muscles depends on electrical impulses that are controlled by the distribution of electrolytes within and outside of each cell. Electrolytes serve two functions essential to life:

  1. They mediate electrical impulses to stimulate muscle contraction and movement.
  2. They regulate the balance of body water within the various fluid compartments.

Also, sodium is essential to drive the thirst reflex so a horse will drink to replace fluid losses.

Electrolyte Replenishment

Let’s look at some sources for electrolytes commonly lost in sweat:

  • Potassium – abundant in grass or alfalfa hay
  • Calcium – especially abundant in alfalfa hay
  • Magnesium – especially abundant in alfalfa hay
  • Chloride – needs to be provided as supplemental salt
  • Sodium – needs to be provided as supplemental salt

In general, 1–2 ounces of salt is given periodically through an endurance-type event, ideally supplemented at a time when a horse takes a good drink, or in the case of long-distance ride, roughly every 15-20 miles. A combination of three parts table salt (NaCl) and one part Lite salt (KCl) makes an appropriate mixture. There is no specific recipe for the amount given and the frequency of administration; that depends on:

  • The ambient weather conditions
  • The fitness of your horse
  • The effort of the exercise demand based on terrain and speed
  • The duration of the event
  • Length of the course
  • Number of consecutive days ridden
  • How well your horse is drinking
  • Number of rest stops allowed for eating and drinking
  • Condition of the horse after transport to the event

Research done on distance riding events reveals that the greatest loss of fluids and electrolytes occurs within the first 20 miles. In contrast, a horse that sweats during a relatively short training ride or equitation efforts in an arena might lose some body water and a small degree of electrolytes, but the exertion is quickly over. In a short time, he easily replenishes what was lost without supplementation, especially with access to hay and a salt block.

For more extreme athletics in intensity and duration, water and salt replenishment is important to stay ahead of the losses and to maintain efficient muscle function so your horse performs safely and with enthusiasm for his work. For equestrian activities that benefit from electrolyte supplementation, success relies on proper conditioning and preparation, an intelligent riding strategy, and constant vigilance as to how well your horse is coping with the exercise effort. 

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