Like humans, horses sweat to dissipate heat. Horses sweat excessively during very hot conditions, and when they have been exercised intensely, especially when they are unfit. Horses also sweat when they have a high fever or are in pain or distress. This loss of fluids from excessive sweating itself result in dehydration, which can cause worsening of systemic illness.

A thick white foamy type of sweat, often referred to as "lather" or "soap", is the excretion of fluids, electrolytes and proteins. Often, horses will perspire in this manner if overexerted (exercised beyond their fitness level) and/or stressed.

If your horse seems to be sweating inappropriately, you can begin gathering important information to discuss your concerns with your vet. Assess your horse's general health using the Whole Horse Exam (WHE). Look for other signs of illness or injury that might underlie the sweating. Pay attention to drinking and eating habits and hydration. Take some time to notice when sweating occurs. Is it associated with exercise or hot weather, or does it occur at odd times, seemingly independent of exercise or temperature? Does the horse sweat all over or only in specific localized areas.

Take the heart rate immediately after intense exercise, and 10 minutes later. The heart rate should have dropped to a minimum of 60 BPM at 10 minutes post-exercise. Consider their performance and conditioning generally. Has it changed?

If the horse seems to be sweating inappropriately under saddle, consider whether they are fit enough for their level of exertion. Share all of your findings and concerns with your vet. All of this is important information that may help your vet in determining the underlying cause and potential solutions.

WHAT YOUR VET DOES
In addition to routine examination, blood work can be very useful in better understanding electrolyte balance.