Foaming at the Mouth in Horses: Guide to Equine Hypersalivation (Ptyalism)

Horses produce between five and ten gallons (20 to 40 litres) of saliva each day. Saliva is vital for moistening and lubricating food, facilitating easier swallowing, and neutralizing stomach acid. Unlike many other animals, horses only produce saliva during mastication (chewing).

Horse saliva contains latherin, a protein that aids in thermoregulation and may contribute to digestion of coarse fibers. Latherin causes the production of “happy foam,” a froth-like substance formed during chewing, generally considered a sign of good health in horses.

Several conditions and situations can lead to disruptions in normal equine salivation. While generally not life-threatening, these changes can indicate underlying issues ranging from poisoning to discomfort with the bridle and bit.

Understanding the physiology of salivation and possible risk factors associated with abnormal foaming at the mouth can help horse owners accurately identify the need for veterinary intervention.

Saliva and Digestion

In optimal conditions, horses spend approximately three-quarters of their day eating, and their natural feeding habits are closely tied to the physiology of their digestive system.

Horses are hindgut fermenters, meaning they have a relatively small stomach and the majority of their digestion occurs in the large intestine and cecum. The horse’s digestive tract is highly adapted to a diet rich in fiber and is divided into eight main sections: ^[1]

• Mouth
• Esophagus
• Stomach
• Small Intestine
• Cecum
• Large Colon
• Small Colon
• Rectum

The first stage of digestion begins in the mouth, which is responsible for four essential functions: ^[1][2]

• Grasping food (prehension)
• Chewing
• Salivating
• Swallowing

Unlike ruminants (such as cows and sheep), horses are monogastric herbivores, meaning they only have one stomach. The small size of the horse’s single stomach means food needs to be adequately crushed by the teeth before swallowing. The horse’s powerful jaws work with their specialized teeth to break down fibrous plant material into digestible pieces. ^[1][2]

Another vital function of the mouth is the production of saliva, which moistens and lubricates food, forming a bolus that facilitates easier swallowing. Saliva also neutralizes gastric acid, protecting the stomach lining and maintaining the pH level for optimal digestion. ^[1][2]

Saliva Production in Horses

A distinct aspect of the horse’s digestive system is its saliva production. Unlike many other animals, including humans, horses only produce saliva during mastication or chewing. This physiological nuance lies in contrast to the constant production of equine stomach acid. ^[3]

Horse saliva contains high levels of bicarbonate, which neutralizes high acidity in the horse’s stomach, reducing the risk of ulceration. ^[1][4] Saliva is produced in the salivary glands, and horses have three main pairs: ^[3]

• Parotid: the largest of the horse salivary glands, these are located between the lower jaw and the first vertebra at the back of the mouth; they produce the majority of the horse’s saliva
• Mandibular: lie along the jaw towards the rear of the mouth
• Sublingual: located at the front of the mouth between the tongue and the lower jaw

Foamy Saliva

Unlike human saliva, which is mainly composed of salts, horse saliva is rich in protein. Among the proteins in horse saliva, the most notable is latherin.

Latherin is a non-glycosylated surfactant, meaning it produces foam when subjected to friction. This detergent-like protein is found in equine sweat and saliva, and gives both bodily fluids their characteristic foamy frothiness. ^[5][6]

Latherin plays a role in thermoregulation, helping horses maintain an average body temperature. It is believed to function as the wetting agent in sweat, which prevents overheating through evaporation. Due to their thick, waterproof coats, horses rely on latherin to rapidly transport sweat from the skin to the coat’s surface. ^[5][6]

The role of latherin in horse saliva is not fully understood, but it may aid in the digestion of coarse fibers and control the mouth’s microbial biofilms. Similar to its manifestation in sweat, latherin in saliva forms a froth-like substance known as “happy foam” when friction occurs. ^[6]

A certain amount of foam is not only safe but often desirable. The absence of foam can indicate stress, poor head posture, an ill-fitted bit, poisoning, and a variety of other conditions. ^[6]

Foaming at the Mouth in Horses

Horses produce between 20 and 40 litres (5 – 10 gal) of saliva each day. Saliva plays an important role in digestion as it moistens and lubricates food, aiding its passage from the mouth into the stomach, and protects the stomach lining from acidic gastric juices. ^[1][4]

Excessive salivation, medically referred to as ptyalism, in horses can be attributed to two primary causes:

• Abnormally high production of saliva
• Difficulty swallowing

All of the causes and conditions associated with equine ptyalism relate back to one of these primary mechanisms.

Causes of ptyalism fit broadly into one of these categories:

• Issues with the bit
• Oral conditions or injuries
• Poisoning
• Infectious disease

Issues with the Bit

Bits have been used for centuries to train and direct horses while riding. A bit works with a bridle and reins to apply pressure to the mouth and reinforce other signals from the rider. While bits can often produce a healthy mouth of “happy foam,” they can also cause excessive salivation and inhibit swallowing.

The bit can trigger the horse’s parasympathetic nervous system, restricting tongue movement and leading to an increase in saliva production. In extreme cases this makes swallowing harder and increases the risk of saliva aspiration into the lungs. ^[6]

Always make sure the bit is well fit and appropriate for your horse’s discipline, abilities, and level of training. Work with a qualified professional if your horse is showing signs of discomfort with the bit and consider seeking veterinary attention if the root cause isn’t obvious.

Oral Conditions and Injuries

Several mouth and dental disorders can cause excessive drooling in horses due to difficulty swallowing. These include ^[7][8]:

• Missing, loose, or fractured teeth
• Excessive plaque
• Tartar
• Periodontal inflammation
• Misaligned teeth or bite

Dental disorders are frequent in horses and can lead to significant discomfort and potentially severe secondary infections. All adult horses require dental check-ups at least once a year and regular floating to keep their teeth functional and healthy. ^[9]

Foals and horses under the age of five may require more frequent check-ups as their teeth and mouths are constantly changing. Elderly horses and those suffering from pre-existing dental conditions need regular monitoring. ^[9]

Poisoning

Hypersalivation in horses is often the body’s first response to ingesting toxic compounds. The main form of poisoning associated with excessive salivation in horses is slafranine poisoning (slobbers). Other potential sources of poisoning include:

• Organophophates
• Lead
• Arsenic

Organophosphate toxicosis

Organophosphate (OP) pesticides are widely used insecticides that pose a health risk to horses and other mammals. Horses are at risk of dermal (skin), inhalation, or oral exposure to OP-containing pesticides.

Symptoms of OP toxicosis appear rapidly, within minutes or hours of exposure, and include: ^[10][11]

• Colic
• Diarrhea
• Excessive salivation
• Excessive eye watering
• Excessive urination
• Coughing
• Ataxia (incoordination)
• Muscle twitching
• Lethargy

With prompt and appropriate treatment, the prognosis is generally good, with most symptoms resolving within 48-72 hours after onset. However, horses that present with paralysis or seizures carry a guarded prognosis.

Lead Poisoning

Lead ingestion can cause excessive salivation in horses. Ingestion of lead poses a significant health risk to both horses and other mammals, including humans.

While cattle and dogs are often more severely affected by lead exposure, horses can suffer from lead poisoning, usually after grazing on contaminated pastures. Improper disposal of industrial waste is the primary source of environmental lead contamination. ^[10][12][13]

Depending on exposure duration and the size of the dose, horses may develop either acute or chronic lead poisoning, both of which can result in severe health complications and potentially death.

Symptoms of lead poisoning include: ^[10][12][13]

• Colic
• Lethargy
• Abnormal tongue movements
• Weight loss
• Weakness
• Diarrhea
• Seizures
• Lack of appetite
• Laryngeal paralysis (roars)
• Difficulty swallowing
• Collapse
• Lameness

While a simple blood test can identify lead poisoning in horses, the rarity of the condition means a veterinarian is likely to focus on more common conditions that may cause similar symptoms during investigation. This is why providing a detailed history of the horse’s environment is an important step for accurate and speedy diagnosis.

Once diagnosed, treatment involves administering an antidote, general care, and detoxification. The prognosis varies in accordance with the amount of lead ingested. Severely affected horses often have a poor prognosis. ^[10][12][13]

Arsenic Poisoning

The ingestion of arsenic, a non-metallic element, is also associated with excessive salivation in horses. Arsenic is found in trace amounts in most soils and has historically been used in feed additives, wood preservatives, and herbicides.

Currently, arsenic is a heavily regulated substance in the United States and it is no longer in widespread use in manufacturing. However, outdated arsenic-containing products continue to pose a risk to horses. ^[10][14][15]

The horse’s gastrointestinal tract rapidly absorbs soluble arsenic compounds, which enter the bloodstream. There, they bind to red blood cells and get distributed throughout the horse’s body, interrupting cell metabolism and overall function. ^[10][14][15]

Arsenic poisoning in horses typically presents acutely, causing cardiovascular collapse shortly after exposure. Horses that survive may exhibit signs of kidney damage, including low urine output. Diagnosis relies on history of exposure and ruling out other conditions that may cause similar symptoms. ^[10][14][15]

Emergency treatment involves immediate removal from the arsenic source. Prognosis depends on the severity of the toxicosis; most horses that survive initial symptoms are likely to recover. Preventive measures, such as careful reading of product labels and proper disposal of arsenic-containing items, are fundamental to horse safety.^[10][14][15]

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Slaframine Poisoning: Slobbers

A common cause of excessive salivation in horses is slaframine toxicosis, commonly referred to as slobbers. Slaframine poisoning is caused by consumption of forages contaminated with slaframine, a toxic secondary metabolite produced by the Slafractonia leguminicola fungus.

The fungi most commonly attach to plants belonging to the clover family, especially red clover (Trifolium pratense), but other forages may be infected. ^[16][17]

Following the ingestion of a contaminated plant, slaframine is metabolized in the liver and is converted into an active compound that binds receptors that regulate the salivary glands.

The onset of symptoms occurs rapidly, generally two to six hours from ingestion, and include: ^[16][17]

• Copious amounts of saliva dripping from the mouth
• Excessive eye discharge
• Excessive urination
• Difficulty swallowing
• Dehydration
• Choking

Affected horses tend to recover rapidly (24 – 48 hours) after removal of the contaminated foliage and generally do not require medical attention. Access to plentiful water is critical to recovery due to the slaframine-induced fluid loss. ^[10][17]

Infections

Both bacterial and viral infections can cause horses to produce excessive amounts of saliva. The most well-known infectious diseases associated with ptyalism in horses include:

• Rabies
• Strangles
• Vesicular stomatitis

Rabies

While rare in horses, rabies is a fatal infection that can cause, among other symptoms, foaming at the mouth.

Rabies is an acute viral infection that affects the nervous system, leading to severe symptoms and, ultimately, death. The virus is transmitted to horses by bites from common carriers of the virus, including raccoons, skunks, bats, and foxes. ^[4][18][19]

Horses primarily exhibit the ‘dumb’ or paralytic form of rabies. This form typically involves paralysis of the throat and jaw muscles, resulting in excessive salivation and inability to swallow. Other symptoms include: ^[4][18][19]

• Lethargy
• Paralysis
• Drooping of the face or jaw
• Foamy saliva

The onset of clinical signs ranges from two to six weeks following exposure; once symptoms occur, they progress rapidly and lead to sudden death. ^[4][18][19]

Strangles

Strangles is a highly contagious respiratory bacterial infection endemic to the UK. The infection is caused by Streptococcus equi bacteria, which can infect all equine species, including horses, ponies, and donkeys.

The bacteria primarily target the lymph nodes, leading to a range of symptoms that can vary significantly in severity, including: ^[4][20]

• Excessive salivation
• Loss of appetite
• Fever
• Cough
• Swollen lymph nodes
• Swollen pharynx (throat)

Horses diagnosed with strangles require supportive care. Treatment for strangles focuses on managing symptoms; options include: ^[20]

• Stall rest
• Anti-inflammatory medications

While antibiotics are rarely used to treat strangles, they may be prescribed in severe cases or if the infection spreads to other parts of the body. Due to the highly contagious nature of the infection, it’s important for farms to leverage robust biosecurity and quarantine protocols when horses are recovering from strangles. ^[20]

Vesicular Stomatitis

Vesicular stomatitis is also associated with ptyalism in horses. This illness is caused by the Vesiculovirus virus, and is a zoonotic infection, meaning it can be passed from animals to humans. ^[21][22]

The virus is spread through direct contact with infected animals, contaminated equipment, or indirectly by insect bites. In horses, the incubation period ranges from two to eight days. Excessive salivation is the first and most noticeable symptom; it occurs as the result of the formation of ulcers in the affected horse’s mouth, tongue, lips, and nostrils.

Other clinical signs include: ^{[4][21][22][23]}

• Fever
• Lethargy
• Lack of appetite
• Lameness

Diagnosis of vesicular stomatitis is based on clinical signs and confirmed through laboratory tests. To date, there is no specific treatment for vesicular stomatitis. Treatment is primarily supportive and involves: ^[21]

• Providing soft feed to reduce oral discomfort
• Ensuring adequate hydration
• Maintaining good hygiene to prevent secondary bacterial infections

Infected horses should be isolated to prevent the spread of the virus. The prognosis for vesicular stomatitis is generally good, with most horses recovering within two weeks. Preventive measures include implementing pest control programs and maintaining good biosecurity practices.

Concurrent Symptoms

Depending on the underlying cause of the excessive salivation, horses may present several concurrent symptoms that may vary in severity: ^[10]

• Decreased appetite
• Oral abrasions
• Fever
• Oral ulcers
• Difficulty swallowing
• Lesion of the lip junctions
• Lethargy
• Behavioral changes
• Convulsions
• Discomfort
• Lameness

Risk Factors

Several factors can increase the risk of horses presenting with excessive salivation, slobbers, and foamy saliva; these include: ^[5]

• Nutrition; horses fed mostly high protein or grain feed produce less saliva
• Inappropriate or poorly fitting bits
• Environmental conditions
• Stress
• Vaccinations status

By addressing these risk factors and providing appropriate treatment when warranted, caretakers can ensure horses maintain optimal health and comfort. Regular veterinary care, proper nutrition, and good management practices are vital to preventing and managing excessive salivation in horses.

Prevention

In many cases, horses foaming at the mouth is a normal, healthy biological process that does not need to be prevented or managed. Preventing conditions associated with clinically relevant hypersalivation requires a multifaceted approach due to the array of conditions associated with this symptom.

General preventative strategies include:

• Keeping up to date with vaccinations, dental care, and routine fecal testing
• Regular veterinary checks to promptly identify and address potential health issues
• Frequent monitoring to avoid contaminated or inappropriate forage that could cause slobbers
• Providing a balanced, forage-based diet

Summary

Saliva, a fluid produced by the salivary glands, plays a central role in the first stages of digestion. Horses foaming at the mouth is often a normal, healthy process, but some health conditions are associated with hypersalivation (ptyalism) and warrant veterinary attention.

• Common conditions that can cause excessive salivation in horses include slaframine poisoning, dental and oral cavity issues, ill-fitting bites, infections, and mechanical injury.
• Foamy saliva is caused by latherin, a detergent-like protein present in horses’ sweat and saliva. When subjected to friction, latherin produces foam.
• Several other symptoms can accompany excessive salivation depending on the underlying cause, including anorexia, fever, depression, lameness, difficulty swallowing, and oral ulcers.
• If your horse is foaming at the mouth, consult with your veterinarian to obtain an accurate diagnosis.