Is My Horse Sweating Too Much or Not Enough? – [Abnormal Perspiration Guide]

In hot conditions or during exercise, horses sweat to cool down. Sweat evaporation dissipates anywhere from 65 – 70% of excess body heat from the horse’s body. This process is one aspect of how horses control their internal body temperature, referred to as thermoregulation.

Horses can produce 4 gallons (15 litres) of sweat per hour or even more. ^[1] Equine sweat contains water, electrolytes and proteins like latherin which aids in sweat transport through the horse’s waterproof coat.

Although horses are known for producing high volumes of sweat during exercise, in some instances excessive sweat or a lack of perspiration is a symptom of an underlying medical condition.

Excessive sweating is associated with conditions like tying-up and colic, while inability to sweat is a condition itself (referred to as anhidrosis).

It’s helpful for horse owners and caretakers to familiarize themselves with the difference between healthy and abnormal sweating so they can make timely decisions when medical intervention is required.

Why Do Horses Sweat?

Thermoregulation is the process by which all mammals, including horses, keep their body temperature stable within a normal range for their species.

Horses are endothermic or warm-blooded (not to be confused with warmblood breeds) meaning they produce body heat internally. As the body’s cells perform metabolic functions, heat is released. ^[2] Heat is also produced through digestion and fermentation of feed in the horse’s gut.

Genetically well-suited to cold weather, horses can maintain their core body temperature with almost no energy expenditure even in temperatures as low as 40°F (4.4°C). This resilience is due to their ability to grow a thick coat and accumulate additional fat in the months leading up to winter. ^[3]

Conversely, when in hot environments or when subject to high levels of physical activity, horses sweat to keep their temperature within the correct range (99 – 101°F or 37.5 – 38.5°C). ^[4]

Perspiration

The evaporation of sweat from the skin’s surface allows the horse to dissipate heat. Horses rely on sweat evaporation to dissipate between 65 – 70% of their body’s excess heat, with another 25% dissipated through breathing alone. ^[5][6]

As with humans, horses’ rate of sweating increases relative to environmental temperatures and during exercise. Humidity of the air can also impact sweat rate. ^[7]

Depending on environmental factors and levels of physical activity, horses produce up to 4 gallons (15 litres) of sweat every hour. ^[1]

Sweat Glands

Sweat is produced by the sweat glands; horses have over 800 glands per square centimetre of skin. There are two types of sweat glands: ^[5][8][9]

• Apocrine glands: the most common kind found all over the horse’s body, located in the dermis and connected to hair follicles
• Eccrine glands: only found in the frog of the hoof

When a horse is in a hot environment or exercising, thermoreceptors (temperature sensors) on their skin and in their body sense the increase in temperature. The hypothalamus in the brain senses then stimulates the apocrine glands to sweat. ^[5][8]

Sweat Composition

The exact composition of horses’ sweat can vary depending on several factors including: ^[7][10][11]

• Diet
• Hydration status
• Environmental conditions

Horses’ sweat is primarily composed of water, but it contains other elements including electrolytes such as sodium, chloride, potassium, and to a lesser extent calcium, and magnesium and protein.

Electrolytes

Sweat contains electrolytes which are minerals that carry an electrical charge when dissolved in water.

Electrolytes are found throughout the body, in the bloodstream, and in cells. They play an important role in maintaining fluid balance, transmitting electrical signals in the nervous system, enabling muscle contraction and other physiological functions.

Horses assimilate electrolytes from feed and lose them in sweat and urine. Horses living in hot climates and those in heavy work lose larger amounts of electrolytes due to increased output of sweat.

Electrolyte loss in sweat

In horses, the primary electrolytes lost in sweat are: ^[1][5][12]

• Sodium: ~2.8 g per L of sweat
• Chloride: ~ 5 g per L of sweat
• Potassium: ~ 1.2 g per L of sweat
• Magnesium: ~ 0.1 g per L of sweat
• Calcium: ~ 0.1 g per L of sweat

Latherin

Due to their waterproof coats, horses rely on a unique protein in their sweat, latherin, to transport sweat from the skin to the hair coat’s surface.

Latherin is a type of protein called a surfactant, which means it has detergent-like properties and foams when subjected to friction. ^[13] This protein is also present in horse saliva and is what gives both bodily fluids their characteristic frothiness.

Latherin plays a fundamental role in equine thermoregulation, helping horses maintain an average body temperature through sweat evaporation. ^[13] It is also the reason why horse sweat sometimes looks foamy.

Equine Sweat Scoring

Sweat in horses may be a sign of an underlying medical condition when it is:

• Excessive
• Low output
• Completely absent

Therefore, it’s important for owners and caretakers to familiarize themselves with what a normal sweat response looks like for each individual horse. For horses that are regularly working under saddle, you can use the following visual sweat score to track how sweaty they look under different conditions and exercise regimens.

If you notice your horse sweating much less or much more than you expect, look out for signs of heat stress and consider notifying your veterinarian.

Table 1. Visual Sweat Score for Horses Following Exercise ^[7]

*Based on a 500 kg / 1,100 lb horse

Illustration: Dr. Ana Mesa, PhD

Excessive Sweat

Excessive sweating in horses can result from various conditions affecting the horse’s ability to regulate body temperature or respond to stress. Factors that can contribute to excessive sweating include:

• Genetic disorders
• Metabolic disorders
• Environmental stressors
• Infections or skin conditions
• Ingestion of toxic compounds

Specific conditions associated with increased sweat production include tying up, colic, electrolyte imbalances, and heat exhaustion.

Tying up

Exertional Rhabdomyolysis (ER), also referred to as tying-up, is a condition that causes breakdown of muscle tissue following exercise. Tying-up is categorized as either acute (sporadic ER) or recurring.

Recurring ER is often associated with another condition called Polysaccharide Storage Myopathy (PSSM).

All forms are characterized by muscle spasms and excessive sweating, and in severe cases may lead to collapse. Both forms of ER are medical emergencies requiring prompt veterinary intervention.

In both forms, tying-up is associated with intense exercise. Several risk factors increase the likelihood of a horse developing sporadic ER, including: ^[16][17]

• Exercising after prolonged periods of inactivity
• Nutritional imbalances
• Exercising while sick

Recurring ER due to PSSM is caused by an underlying genetic mutation in the glycogen synthase gene that causes excessive production of glycogen in the muscles. ^[16][17]

Severe cases of PSSM can result in recumbency and life-threatening liver failure. Quarter horses and draft horses are more likely than other breeds to develop PSSM. ^[16][17]

Symptoms

Symptoms of tying up in horses include: ^[16][17]

• Excessive sweating
• Elevated heart rate
• Difficulty breathing
• Pain and stiffness in lumbar and gluteal muscles
• Asymmetrical gait
• Hind limb stiffness
• Reluctance to move

Diagnosis

Diagnosis of sporadic ER and PSSM mainly relies on excluding other potential conditions that may cause similar symptoms. Veterinary specialists may run ulterior diagnostic tests, including: ^[14]

• Controlled exercise test for sporadic ER
• Muscle biopsy for PSSM

Treatment

Treatment focuses on keeping the horse in a safe, secure and comfortable environment, reducing body temperature, and nutritional management. ^[14][15]

The prognosis for sporadic ER and mild cases of PSSM is generally good to excellent. Unfortunately, horses presenting severe episodes of PSSM often die as a result of liver failure. ^[14][15]

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Colic

Colic is a broad term that refers to abdominal pain in horses; it can range from mild discomfort to severe pain recurrence and sudden death.

Horses can present abdominal pain for a wide array of reasons, including: ^[18][19]

• Intoxication – the ingestion of toxic plants can cause sweating, among other symptoms of colic
• Nutritional imbalances – horses fed diets high in grain and low in forage are at a greater risk of developing colic
• Medications (Ionophores, prolonged use of NSAIDs)
• Impaction
• Excessive gas
• Colon shift
• Tumors
• Dental issues
• Dehydration
• Stall confinement
• Worm infestations
• Changes in diet
• Stress

As with underlying causes, symptoms of colic vary greatly from lip curling in mild cases to lethargy and recumbency. If a horse suffering from abdominal pain exhibits excessive sweating, it requires immediate veterinary care as it is a symptom of severe and potentially life threatening colic. ^[18][19]

Concurrent Symptoms

Horses with colic can present several other symptoms together with profuse perspiration including: ^[19]

• Curling the upper lip
• Looking at flank
• Restlessness
• Pawing or kicking abdomen or flank
• Recumbency
• Rolling
• Reduced bowel movements
• Anorexia (lack of appetite)

Heat Exhaustion and Heatstroke

Heat stress in horses occurs when their natural cooling mechanisms fail, often exacerbated by hot, humid conditions or intense exercise. Left untreated, heat stress can progress to heatstroke, a potentially fatal condition characterized by a body temperature exceeding 105°F (40.5°C) in horses. ^[20][21]

Heatstroke is a medical emergency as it compromises organ function and blood circulation. Factors influencing equine heat tolerance include acclimatization, breed, age, diet, fitness, and humidity levels. ^[20][21]

The signs of heat stress in horses include: ^[20][21]

• Elevated body temperature (41 – 43°C / 105 – 109F)
• Profuse sweating
• Increased heart rate at rest (> 48 bpm*)
• Increased respiratory rate at rest (> 14 brpm*)

*Note: Normal heart and respiratory rates vary based on age, body size, and fitness. These values are a general guideline, but normal values for your horse may differ. The best way to track your horse’s normal heart and respiration rates is to monitor them regularly at rest.

Immediate cooling measures, such as moving the horse to a shaded area, cold hosing, and providing water, can mitigate risks. Severe cases require veterinary attention, especially if symptoms worsen despite efforts made to cool the animal. ^[20][21]

Consequences of Excessive Sweating

Regardless of whether excessive sweating has a pathological origin, extreme fluid loss of any kind can result in serious electrolyte imbalances if the electrolytes lost through sweat are not replenished.

Electrolyte imbalances can have a severe impact on the horse’s overall health and function, including:

• Muscle function
• Glucose transport
• Cell metabolism
• Fluid balance

Horses are at particular risk of depleting sodium stores, which is why they need loose salt added to their feed daily.

When a horse is deficient in sodium, it often results in decreased water intake and subsequent chronic dehydration, which can impair performance and health. ^[6][12] Acute dehydration may be related to dietary deficiency in combination with a large loss of fluid, such as through sweating.

Sodium deficiency can be either chronic or acute. Chronic deficiency leads to reduced thirst, loss of skin elasticity, the tendency to lick sweat-contaminated objects, and, in severe cases, anorexia (appetite loss). Horses with acute sodium deficiency present with muscle spasms and wobbly gait. ^[6][12]

The recommendation for an average 500 kg (1,100 lb) horse is to provide 2 to 4 tablespoons of loose salt daily. However, individual needs may vary based on the horse’s body weight, activity level, and climate.

Horses that are exercised regularly or exposed to hot climates need electrolyte supplements to replace the minerals lost through sweating. Electrolyte supplements should be provided in addition to their daily salt provisions.

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Inability to Sweat: Anhidrosis

A significant decrease in sweat rate or the total inability to sweat is a condition referred to as anhidrosis or dry coat in horses. To date, the precise physiology of the condition isn’t fully understood.

Current theories suggest neurological and/or hormonal disruption to the sweating mechanism are involved. ^[21]

This condition primarily affects horses living in tropical climates; in the United States, the majority of reported cases occur on the Gulf Coast (Texas, Louisiana, Mississippi, Alabama, and Florida). The prevalence of anhidrosis in the equine population in the Southern US ranges from 6% to 20%. ^[21]

While most cases occur in tropical climates, horses living in temperate regions can develop the condition during periods of high temperatures. The occurrence of anhidrosis in such areas is likely to increase due to climate change-induced rise in temperatures.

Horses can present anhidrosis in both acute and chronic forms, with chronically affected animals developing sweat gland atrophy. Clinical signs of dry coat include: ^[21]

• Decreased perspiration; some affected horses may still produce sweat in various body regions
• Absent perspiration
• Decreased performance
• Elevated body temperature
• Rapid breathing (tachypnea)
• Alopecia (hair loss)

Diagnosis of anhidrosis is primarily based on clinical presentation and knowledge of the horse’s environment. If needed, veterinarians can administer a specific diagnostic test, which includes the intradermal injection of either terbutaline or epinephrine. ^[21]

Unfortunately, due to the lack of complete understanding of the condition, no specific treatment is currently available. Instead, horseowners can address the symptoms by: ^[21]

• Reducing exposure to heat
• Reducing physical activity
• Electrolyte supplementation
• Feeding additional salt
• Nutritional support; supplementation with vitamin E, ascorbic acid, and cobalt can aid in recovery

While some horses may resume normal perspiration after ten days of environmental management, others may not improve despite receiving symptomatic treatment. ^[14][21]

Horses that do not recover need to be relocated to cooler climates and may suffer from long-term decreased performance or develop life-threatening heatstroke. ^[14][21]

Diagnostics

Diagnosing the underlying condition causing either excessive or lack of sweat secretion is complex, as several factors can contribute these symptoms.

An initial diagnosis is based on a physical examination and medical history. Additional testing to investigate further may include:

• Intradermal injections
• Blood tests
• Diagnostic imaging
• Rectal examination
• Muscle biopsy
• Paracentesis (sampling abdominal fluid)
• Urinalysis
• Controlled exercise test

Treatment

Treatment for abnormal perspiration in horses is related to the underlying conditions causing the perspiration disorder.

Rhabdomyolysis

In cases of tying-up and PSSM, treatment may include: ^[14][15]

• Pain management
• Dietary management
• Administration of sedatives
• Administration of muscle relaxants

Heat Stress

In cases of heat stress and heatstroke, the first goal in treatment is lowering the horse’s body temperature. Strategies include: ^[20][22]

• Hosing
• Sponging
• Applying ice
• Moving to a climate controlled location
• Moving indoors

As with all conditions causing excessive sweating, additional aids in the treatment of heat stress and heatstroke are the administration of electrolytes and rehydration.

Colic

Due to the broad nature of colic and the sheer number of underlying causes that can cause abdominal pain in horses, treatment options vary widely, including: ^[18][19]

• Pain medication
• IV fluid therapy
• Intestinal lubricants or motility medications
• Laxatives
• Surgery
• Deworming

Anhidrosis

Since the causes of anhidrosis are not well understood, treatment is limited and outcomes are variable. Some horses with anhidrosis may respond favorably to: ^[20]

• Heat relief
• Providing ample and clean water
• Increasing salt intake
• Relocation to a cooler climate
• Supplementation of vitamin E
• Administration of electrolytes

Prognosis

The prognosis of conditions that cause excessive or decreased sweating in horses varies greatly depending on:

• The underlying cause
• The horse’s health status
• Severity of symptoms
• Environmental conditions

In all cases, regardless of cause or severity, prompt veterinary attention provides the best chance of a positive outcome. Early intervention can significantly improve the prognosis in many cases by addressing the underlying cause before the condition progresses to a severe phase. Delayed treatment may lead to complications, prolonged recovery times, and death.

Prevention

Due to the wide range of conditions that can cause sweat secretion imbalances, prevention requires a multifaceted approach that takes into consideration nutritional, environmental, and health factors.

Regular veterinary checkups and staying up-to-date with routine vaccinations and appropriate deworming schedules are cornerstones of preventive management and health care.

Environmental management is key in preventing sweat-related disorders, as several conditions that hinder normal sweat secretion are exacerbated or directly caused by excessive heat. Heat management includes:

• Providing shade
• Implementing cooling systems (e.g., fans, misting systems, and air conditioners)
• Providing constant access to a plentiful, clean water source at all times
• Avoid training or work when it is excessively hot

Checking the Equine Heat Index Tool for your location prior to exercising your horse can help you determine the risk of heat stress. Depending on temperature and humidity for your region, exercise modifications may be required to keep your horse safe.

Nutritional management is the third pillar in preventing perspiration-related disorders. Nutrient deficiencies and imbalances can contribute to abnormal sweating.

Understanding each horse’s specific nutritional needs at every stage of growth is key to supporting their health and well-being. Not sure if your horse’s diet is meeting their needs? Submit their diet online for a free evaluation by one of our qualified equine nutritionists.

Summary

Sweat disorders in horses can lead to either excessive sweating or an inability to sweat. Prompt intervention is essential to address both the symptoms and underlying causes.

• Horses are endothermic animals and cool their body through sweating
• The main components of equine sweat are water, electrolytes, and proteins
• Inability to sweat (anhidrosis) primarily affects horses in hot climates, resulting in a dry coat, reduced or absent sweating, high body temperature, and rapid breathing
• Conditions that can cause excessive sweating include colic, tying-up, heat stress, and heat stroke
• Prognosis for conditions that affect sweating in horses varies depending on the cause, severity, and promptness of treatment
• Regular veterinary care, proper nutrition, and environmental management are key to preventing sweat disorders