Hypersalivation (Drooling) in Horses

What is Hypersalivation in Horses?

Saliva, or drool, is the watery liquid that the body makes to help moisten the mouth, lubricate food for swallowing, and aid in digestion. Saliva is made of water, electrolytes, and proteins.

Horses have three pairs of salivary glands; the parotid, the sublingual and the mandibular. In combination, those glands produce about 10 gallons of saliva a day. Hypersalivation occurs when the horse is either producing too much saliva or when the horse is not swallowing the normally produced amount of saliva.

Hypersalivation is an uncommon clinical sign of disease, so when streams of drool are pouring from your horse’s mouth, it is a medical emergency. Causes of hypersalivation can range from a simple dietary mistake to a deadly disease. Contact your veterinarian immediately if your horse is hypersalivating.

Symptoms of Hypersalivation in Horses

• Pool of fluid by your horse

• Reluctance to eat

• Difficulty swallowing

• Repeated attempts to swallow

• Coughing

• Gagging

• Saliva or drool dripping from horse’s mouth

Causes of Hypersalivation in Horses

Rabies

Rabies is a neurologic disease that is caused by a virus that is spread through the saliva of an infected mammal. Although an extremely rare cause of hypersalivation, it should always be considered in cases of excessive drooling since rabies virus is transmissible to humans and is deadly. Horses with rabies often show other signs of disease like depression, weakness, and colic.

Vesicular Stomatitis

This is a rare virus, but is a disease that is reportable to state authorities due to its ability to spread rapidly by flies, ability to transmit to humans, and cause damaging economic impacts. The virus produces blisters on the tongue and mouth which result in the horse hypersalivating due to pain and inflammation. The virus also causes these lesions to develop around the coronet band on the hoof, often resulting in lameness. 

Toxicity

Toxicity is a common cause of hypersalivation. Chemical toxicities are often caused by horses chewing on fence boards or stalls recently painted or treated with wood protecting products. Some plants like buttercups and marigold release chemical toxins that promote the production of saliva. Other plants, like burdock, sandbur, and foxtails, cause physical irritation to the mouth. Although generally uncommon, horses can also be poisoned by maple leaves, black walnuts, and acorns.

Slobbers

The most common cause of hypersalivation is caused by fungus called Rhizoctonia leguminicola that is commonly found in soil and transmitted in seeds. This fungus produces a toxin called slaframine which causes the body to produce extra saliva. It also causes diarrhea, frequent urination, and excessive crying. If left untreated it can be life threatening.

Fractured Bone or Facial Nerve Trauma

A fractured bone in the skull or trauma to the facial nerve can cause hypersalivation. This is usually caused by an injury, like a kick to the head or a severe fall causing traumatic brain injury. Similarly, an ill-fitted halter can apply pressure to the facial nerve and cause injury. Drool is most often seen from the side with the injury and the lip on the affected side will droop.

Strangles

Strangles is caused by an infection with the bacteria, Strepptocoocus equi. It causes swelling in the lymph nodes around the neck which in turn prevent the horse from swallowing normally. You can often see a visible bulge at the base of the neck which are the swollen lymph nodes.

Choke

Choke in horses is caused by an obstruction in the esophagus (food tube). The obstruction is usually composed of food and occurs when the horse does not chew and swallow his food appropriately.

Salivary Gland Diseases

Small stones made from the electrolyte salts in the saliva can form blockages in the salivary glands. Saliva can also accumulate in little cystic pockets called sialoceles. Cancer, especially squamous cell carcinoma, can also spread to the salivary glands.

Mouth Abnormalities

Mouth problems are the second most common cause of hypersalivation after slobbers. As equine teeth wear down, they develop sharp enamel points. These enamel points cause ulcerations on the gums and tongue. Other dental issues like broken teeth or infection can cause hypersalivation too.

Occasionally, horses find foreign material, like sticks, metal fragments, or wire, in their pastures and try to graze on them. These objects can get lodged in the soft tissues of the mouth or in between the teeth and cause pain, irritation, and hypersalivation.

It is recommended to have your horse’s teeth checked by an equine dentist at least once a year.

How Veterinarians Diagnose Hypersalivation in Horses

As with most horse diseases, your veterinarian will perform a full physical exam and take a history. It is necessary to examine your horse’s diet closely. Note any changes or additions to the diet, including whether a new bale of hay or bag of feed was offered. The horse’s environment needs to be examined for any objects the horse may be chewing on or patches of toxic plants.

Diagnostic tests include:

• Physical exam: Other abnormalities like an elevated temperature or decreased gut sounds may help your veterinarian diagnose an underlying cause.

• Oral exam: Your vet will identify wounds, sores, ulcers, or foreign material. As well as inspect the teeth and assess tone and strength of tongue muscles. When your veterinarian examines your horse’s mouth, they will need to wear gloves. This will help prevent the transmission of any disease that may be transferred from horses to humans, for example rabies virus and vesicular stomatitis virus.

• Passing a nasogastric tube: This will rule out an esophageal obstruction (choke).

• Endoscopic exam: An endoscope can be used to locate disease processes located in the guttural pouches, the back of the throat and part of the esophagus.

• Blood work: This is used to look for evidence of inflammation or infection. Specific tests for viral diseases may be sent to a laboratory.

Treatment of Hypersalivation in Horses

Treatment of hypersalivation in horses depends on the cause of the drooling. For example, your veterinarian will need to lavage (wash out) your horse’s esophagus to resolve a choke or they will need to float their teeth or remove a broken tooth to resolve dental abnormalities.

In the case of most toxicity exposures, removing the toxin from the horse or its environment along with supportive care and rest will allow the horse to recover in about one to two weeks.

Horses that have contracted strangles will need to be isolated and treated with antibiotics.

There is no specific treatment for vesicular stomatitis, but with supportive care most horses positively recover.

Unfortunately, rabies is fatal and there is no treatment. That is why it is imperative to have your horse up to date on its rabies virus vaccination and proceed with caution when you encounter a hypersalivating horse.

In general, medical treatments that accompany the specific treatment may include:

• Antibiotics: to fight infection

• Anti-inflammatories: to decrease inflammation, alleviate pain (e.g. phenylbutazone, flunixin meglumine)

• Oral rinses with chlorhexidine: to control infection

• Potassium supplementation: to help replace potassium lost in saliva

Recovery and Management of Hypersalivation in Horses

Most occurrences of hypersalivating in horses will result in a full recovery. The timing of the recovery will be determined by the specific cause but usually is under two weeks. During recovery, allow your horse to rest. It is not recommended to ride them and do not put a bit in their mouth.

Your horse may be reluctant to eat at this time, so a palatable and soft diet should be given; for example, a slurry made from a complete pelleted feed like Tribute Senior Horse Food. Horses that have recurrent episodes of choke or poor teeth made need a food like this the rest of their life.

If left untreated, excessive drooling can lead to metabolic problems which will require more serious interventions. Routine dental care and frequently checking the environment for foreign objects and toxic plants are the best ways to prevent the most common causes of drooling.