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How Much Is That Horse Sweating?By Kentucky Equine Research Staff · September 16, 2013

Hard-working horses sweat as they exercise, and intense or long-duration performance can cause a significant loss of body fluid and electrolytes. Owners need to have a fairly accurate idea of how much sweat the horse has lost so that they can provide enough fluid and electrolytes to be sure that their horses make up these deficits.

Estimates of sweat loss have sometimes been based on the extent and intensity of work the horse has been asked to perform. However, each owner’s idea of light, moderate, and heavy exercise is likely to be slightly different from the way other riders define the same work session.

Researchers at Martin Luther University in Germany recently collaborated in a study designed to evaluate equine sweat patterns after exercise. They used 17 Warmblood mares that were assigned to a light work group or a medium work group. The horses were groomed and weighed before exercise. Immediately after exercise, they were unsaddled and photographed to record visible sweat. The horses were weighed three hours after exercise to determine the amount of weight lost. This figure was corrected for water intake, loss of weight in feces and urine, and estimated respiratory fluid loss. All horses completed each work regimen twice; one horse completed each regimen three times.

Five distinct sweating patterns were noted, and these were matched to sweat loss ranges that corresponded to reductions in body weight. The researchers used the figures to devise a sweat-scoring system that could help riders figure the amount of sweat a horse has lost during a particular exercise period. They proposed a system with five levels of sweat production.

For the first level, the horses would have an area under the saddle that was partly and partly dark, sticky, and moist. The throat area would be sticky and the flanks would be darker than normal. Horses at this level would have lost 1 to 4 liters (1 quart to 1 gallon) of sweat. This is about 0.2 to 0.7% of body weight for an average horse.

For the second level, the horses would have wet areas on the throat and under the saddle. There might be small foamy-white areas at the saddle edges, where the reins contacted the neck, and between the hind legs. Horses at this level would have lost 1 to 7 liters (1 to 1.8 gallons) of sweat. This is about 0.7 to 1.2% of body weight.

For the third level, the horse’s flanks, throat, and areas under the saddle and girth would be consistently wet, and the snaffle ring would leave a clear wet impression on the head. Horses at this level would have lost 7 to 9 liters (1.8 to 2.25 gallons) of sweat. This is about 1.2 to 1.5% of body weight.

For the fourth level, the horse’s throat and flanks would be completely wet. They would have moist, dark wrinkles above their eyes. Fat or heavily muscled horses would show pronounced foaming between the hind legs. Horses at this level would have lost 9 to 12 liters (2.25 to 3 gallons) of sweat. This is about 1.5 to 2.0% of body weight.

Horses in the fifth level would have all the above signs and would be actively dripping fluid above the eyes and under the belly. Horses at this level would have lost 12 to 18 liters (3 to 4.75 gallons) of sweat. This is about 2 to 3% of body weight.

Factors like air temperature and humidity may obscure signs of heavy sweating. On windy days when sweat evaporates almost as fast as it is produced, riders may notice only a damp spot under the saddle, even when the horse has worked fairly hard. At other times when the weather does not favor quick evaporation, the horse may be dripping obvious amounts of sweat after an exercise period. Unfit horses may sweat more and earlier in a workout than horses in better condition. Finally, it may be difficult to measure the extent of sweat production when horses have a heavy hair coat because of seasonal variations or health conditions like Cushing’s syndrome. Weighing a horse before and after exercise is one way to evaluate the amount of weight lost through sweating and respiration.

Most commercial electrolyte preparations have directions as to how much to give a horse after various levels of exercise. Replacing electrolytes lost in sweat is important because these substances are necessary for normal body function and will help to prevent conditions such as dehydration, muscular weakness, overheating, tiredness, and poor performance.

Always allow horses access to clean, fresh water, as drinking is the only way they are able to rehydrate after intense exercise. If powdered electrolyte is added to the horse’s water, be sure to offer untreated water as well.