Horse Health: Heat, humidity demand special attention

It is a good time of year to discuss water and exercise. Summer is usually the prime time of year for most of us to ride our horses. It is also the time of year when most of the competitions are held.

Although warm weather encourages us to spend extra time in the saddle, it also demands extra caution in caring for our horses and providing for their water needs. A lack of water will have a more profound and immediate effect on the well-being of the horse than any food nutrient.

The body can lose nearly all of its fat and over half of its protein content and survive. Yet, a loss of 1/10th of the body's water can result in serious consequences.

Supplying adequate water when it is needed can present some challenges for many horse owners. First off, how much water is required? A mature horse (about 1,100 pounds) requires eight to 12 gallons of water a day, and that would be on a cool day with low humidity. The amount required for maintenance is easily altered by the ambient temperature, relative humidity, type of feed, horse health and condition, or type of activity or production.

Exercise in hot, humid weather will increase the maintenance requirement. Moderate work may increase the water requirement 60 to 80 percent and hard work by as much as 120 percent.

A mare in lactation will also need more water for milk production. Feeding large amounts of dry feeds (hay and/or grain) usually increases water needs as well.

Conversely, horses grazing on lush, green pastures may meet most of their requirement from the water in the grass.

Highly digestible feeds may also decrease water intake. High-fat diets may decrease water requirement because of its lowering the heat load from digestion, commonly referred to as the heat of digestion.

High-protein diets or diets with a high salt content will increase the water intake.

In addition to these dietary factors, exercise has the greatest influence on the amount of water required. More than 80 percent of the dietary energy metabolized results in heat production.

Exercise increases the amount of heat the horse must dissipate to function. An inability to dissipate the heat load results in an increase in body temperature to a level that decreases performance and may endanger the horse. Without the ability to dissipate heat, exercise such as trotting would increase body temperature 0.6 degrees a minute and sprinting would increase it 1.2 degrees a minute. This would increase the body temperature to a life threatening 106 degrees in as little as four to six to minutes.

The horse dissipates this heat load primarily through evaporative cooling. Air movement helps with evaporative cooling. Although the horse will still lose heat by evaporative cooling at ambient temperatures greater than body temperature, high humidity severely depresses the evaporative efficiency.

The ability to dissipate heat may be decreased in horses in poor condition, or which have a heavy hair coat, or which are overly fat. These same conditions may also increase heat production, adding to a heat-loss problem.

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

Sweat contains a protein with detergent-like properties that enhance heat loss by evaporation. This is one reason that 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.

Although sweat plays a critical part in thermoregulation, it does have a downside. Sweat contains sodium, chloride, potassium, calcium and magnesium, collectively known as electrolytes.

Excessive sweating and reduced water intake may quickly result in dehydration. Signs of dehydration include sunken eyes, lack of saliva, dry feces, and decreased urination.

Decreased water intake coupled with excessive sweating may result in a decrease in performance at best or may even result in a life-threatening situation. The gastrointestinal tract is the only "storage" place for water or electrolytes.

Excess water or electrolytes absorbed from the GIT are excreted in the urine. There is no way to "stockpile" extra water or electrolytes by providing them before exercise. Severe deficits can be prevented by replacement as they are lost. This is why water, salt, and electrolytes should always be available to the horse during hot conditions or during heavy exercise.

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

■ Tim Potter is an agent with the N.C. Cooperative Extension Service in Forsyth County.