Water, Electrolytes and the Performance Horse

By Richard G. Godbee, Ph.D., PAS, Dipl. ACAS-Nutrition Central Garden & Pet Company/Farnam Companies, Inc.
Courtesy of Farnam.com

It is a good time of year to discuss water and exercise. Summer is the time of year for most of us to ride more and to compete with our horses. While warm weather encourages us to spend extra time in the saddle, extra caution is required for caring for your horse’s watering needs.

Dehydration has a profound and immediate impact on the well-being of the horse more than the lack of any other nutrient. To put it into context, the body can lose nearly all of its fat and over half of its protein content and survive, but a loss of just 1/10th of body water can result in serious consequences.

On a cool day with low humidity, a mature horse requires 8 to 12 gallons of water per day for maintenance. That amount is easily altered by type of feed, type of physical exertion, the ambient temperature relative humidity, and the overall health and condition of the horse.

How Feed Affects Water Requirement
Feeding large amounts of hay and/or grain usually increases water needs. High protein diets or diets with a high salt content will increase the water intake. Conversely, horses grazing on lush, green pastures may meet most of their requirement for water from the grass as it may contain 60% to 80% water. Highly digestible feeds may also decrease water intake. A high fat diet may decrease water requirement because it lowers the heat load from digestion (commonly referred to as the heat of digestion or heat increment).

How Exercise Affects Water Requirement

Exercise in hot, humid weather may increase the maintenance requirement 300% to 400%. Moderate work may increase the water requirement 60% to 80% and hard work by as much as 200%. Over 80% of the dietary energy metabolized results in heat production. Exercise increases the amount of heat the horse must dissipate in order to function. An inability to dissipate heat results in an increase in body temperature to a level that decreases performance and may endanger the horse. Without the ability to dissipate heat, moderate exercise, e.g., trotting, for a certain amount of time time or distance or speed would increase body temperature 0.6°F/minute, while sprinting would increase it 1.2°F/minute. In either case this heat production would increase the body temperature to a life threatening 106°F in as little as 4 to 6 minutes. Fortunately, this is a very rare occurrence.

Horses dissipate heat load primarily through evaporative cooling. Sweating and the respiratory tract account for 55% to 60% and 25% of the evaporative cooling, respectively. Air movement also helps with evaporative cooling. While the horse will still lose heat via evaporative cooling at ambient temperatures greater than body temperature, high humidity severely depresses the evaporative efficiency.

Slightly more than 1 quart of sweat will dissipate the amount of heat produced by trotting for 7 to 8 minutes. During intense exercise, horses can lose significant amounts of fluid through sweat.

How to Determine “Comfort Index” and Hydration

To find out if your horse is at risk, add the outdoor temperature with the relative humidity. If that figure is over 150, there is a potential for overheating and extra caution should be observed. Excessive sweating and reduced water intake may quickly result in dehydration. Signs of dehydration include a slow capillary refill time and a decrease in skin elasticity. To measure the capillary refill time, press your finger on the horses gums, then release your finger and determine how long it takes for color to return. Normal capillary refill time is 1.5 to 2.0 seconds.

A skin pinch, preferably done over the shoulder, should recede in less than 1 second. The skin over the neck is not a good choice to use in checking skin elasticity since it tends to be looser and stand up more easily. Other signs of dehydration may include sunken eyes, lack of saliva, dry feces, decreased urination, increased hematocrit and increased plasma protein concentration.

Sweat contains a protein with detergent-like properties that enhances heat loss via evaporation. This is one reason wiping off sweat is counterproductive. Prolonged sweating results in a watery sweat that is not as effective in dissipating heat.

Running cool water over the horse’s body is a great way to enhance cooling. Begin at the lower legs and work your way up and over the back, shoulder and neck. When using this method of cooling the horse, it may be better to not “scrape” away the water but let it evaporate.

Horse sweat contains 3 times the sodium and chloride, and 10 times the potassium found in human sweat. This is one reason electrolyte products designed for humans, e.g., Gatorade®, are not great choices for horses. Monitor the hydration status of your horse. Know the normal temperature, pulse, and respiration of your horse. Remember each horse is an individual.



  • Provide free access to palatable water. Cool water is preferred because it results in the stomach emptying faster.
  • Monitor intake. A flow meter may be added to the water line of an automatic water flow.
  • Clean buckets and troughs regularly.
  • Understand the relationship between the type of feed and water intake. Horses kept on a lush pasture will probably drink less water than those fed hay.
  • During exercise, allow the horse to drink as often as possible.
  • After exercise, a hot horse should be cooled before allowing free access to water.
  • Use running water to cool your horse during hot weather, especially if the sweat is thin or watery.


  • Provide salt in a loose form to encourage adequate water consumption and help maintain electrolyte balance. If pastured, one to two ounces per day is good. Free choice salt for horses that spend most of their time in a stall usually results in over consumption of the salt and increased water intake and urinary output. This may result in an increase in bedding cost.
  • Gels or paste are excellent means to carry an electrolyte with you on the trail or when away from the trailer or barn.
  • A powder electrolyte is a good choice to use when adding electrolytes to the feed. If a quality electrolyte, e.g., Apple EliteTM product is not available, a mixture of table salt and lite salt in equal amounts may be used. Give your horse 2 ounces every 2 hours during and after work, and ensure water is available. In either case, sodium chloride and potassium chloride should be in the first 4 ingredients. Calcium and magnesium, along with small amounts of iron, copper, zinc, manganese and sometimes cobalt should also be supplied in the product.
  • A small amount of sugar may be beneficial in decreasing the absorption time.
  • Give your horse free access to salt even when using electrolytes.
  • It cannot be over emphasized to supply sufficient water anytime you give electrolytes.
  • Do not add electrolytes to water. This usually results in a decrease in water intake due to the unpalatable saltiness in the water (unless your horse is used to this).

Supplying sufficient water, judicious use of electrolytes and using common sense during hot weather will maximize the performance of your horse while insuring his safety.