Understanding decreased energy and performance in hot weather

Gradually acclimate your horse to increases in work duration and intensity in the summer months.

A common concern this time of year among performance horse caretakers is that their horses seem to lack energy for exercise. If there are no apparent health or lameness issues but the horse is either “flat,” or starts out well but then hits a wall that is at a level of exercise below where they normally perform, the answer could be that it’s just too hot!

The horse is a large animal, and this makes it difficult to dissipate heat. Horses expected to work in the heat should be gradually accustomed to it by stepwise increases in work duration and intensity. Use a heat index calculated by adding the temperature (in degrees Fahrenheit) and the relative humidity. If the heat index is 120 or less, there should be no barrier to heat dissipation. However, if the heat index is 150 or higher, especially with high humidity, the horse will have some difficulty cooling. At a heat index over 180, cooling mechanisms are severely compromised, and the horse should not be worked. Flagging energy and slowing down will be the first sign your horse is overheating. Heed this warning.

Is fluid topped off?

Exercise research has documented that as little as two percent dehydration will compromise performance. Work at low and moderate speeds will affect a horse more than high intensity efforts. This level of dehydration occurs even before you can detect a problem with the skin pinch test so it’s easy to see how dehydration can easily be a problem with work in the heat.

Providing plenty of fresh, clean water is obviously important to avoiding dehydration – but it’s not the whole story. To retain that water in the body the horse needs adequate sodium. The major electrolyte lost in sweat is sodium and it is also highly deficient in both hay and concentrate feeds.

Use a 2-2-2 rule to help guard against dehydration: two ounces of salt the night before a competition or heavy work, two ounces the morning of, and replenish with an electrolyte correctly balanced for sweat if the work is longer than two hours.

Is the gas tank full?

Many horse caretakers today are feeding diets designed to limit starch and sugar intake.  There is much to be said for this, but it can sometimes backfire if the horse is in regular work. The major fuels for muscle work are fat and glucose, with branched chain amino acids also contributing. The fat for muscle work is liberated from fat deposits throughout the body and there is never a shortage. Glucose is taken from the blood, but primarily from glucose stored in the muscle as glycogen. Glycogen in the liver is also used to keep blood glucose normal. Glycogen stores are limited so this is the fuel with the potential to limit work. Fat cannot be used to replace glucose. There is always a baseline glucose requirement.

Glycogen stores are lowered by work and need to be replenished. The very low sugar and starch diet may not be able to keep up with losses. Timed feedings can get maximum benefit from a higher carbohydrate meal and also avoid aggravating insulin resistance. Feed 1 to 1.5 pounds of beet pulp (dry weight) with 1 to 1.5 pounds of plain oats within the first hour after work is finished.

There is a window after exercise where muscle takes up glucose very readily. Even insulin resistant horses can receive extra carbohydrate in that time frame. The oats are easily digested to glucose to begin replacing glycogen. The beet pulp is fermented to acetate, which is more slowly released and can be used instead of glucose for energy functions, freeing up glucose for glycogen. Studies have confirmed acetate supports the glycogen replacement process. As a plus, you can get water and electrolytes into the horse at the same time, which research has shown is also important for replenishing glycogen.

Electrolytes, the battery of life

Electrolytes are minerals existing in the body in an electrically charged, ionized form. Those with positive charges are called cations; negative charges are anions. Electrolytes direct the movement of water throughout the body, and in and out of cells.

A host of essential body functions depend not only on the presence and precise concentrations of electrolytes. These include:

  • The production and secretion of sweat, saliva, intestinal tract fluids, urine and mucus
  • Heart contraction
  • Intestinal movement (and other involuntary smooth muscle contraction, such as the uterus)
  • Absorption of nutrients across the intestinal wall and into the body cells
  • Skeletal muscle contraction
  • Nerve function
  • Maintenance of normal acid-base balance (pH)
  • Maintenance of normal hydration (the body containing roughly 70% water)

Sweat can be a major source of electrolyte loss but there are daily losses in urine, manure and mucus that occur all year. Potassium, sodium and chloride are the major electrolytes of concern. Most hays provide potassium concentrations three to four times higher than needed so unless sweating heavily, a horse getting plenty of hay or pasture will not need potassium supplementation.

Sodium and chloride are another story. Sodium is the major electrolyte holding water in the body. Levels are very low in the diet. Hay/pasture is the major source of chloride, but levels may be borderline and horses not getting generous amounts may be deficient.

Plain salt is sodium chloride. An average-sized adult horse requires a minimum of one ounce of salt per day in cool weather and two to four ounces per day in hot weather. Instead of a brick, add salt to meals or dissolve and spray on hay. Use coarse, loose salt in a separate small feeder for additional free choice intake.

The above explanations account for the vast majority of horses with energy concerns in the summer.  If you are having problems, consider them first.


Dr. Eleanor Kellon, staff veterinary specialist for Uckele Health & Nutrition, has been an established authority in the field of equine nutrition for over 30 years, and is a founding member and leader of the Equine Cushings and Insulin Resistance (ECIR) group, whose mission is to improve the welfare of horses with metabolic disorders via the integration of research and real-life clinical experience.  Prevention laminitis is the ultimate goal. ecirhorse.org
Uckele Health & Nutrition, maker of CocoSoya, is an innovation-driven health company committed to making people and their animals healthier. On the leading edge of nutritional science and technology for over 50 years, Uckele formulates and manufactures a full spectrum of quality nutritional supplements incorporating the latest nutritional advances. uckele.com