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Pet Owner Version

Disorders of the Mouth in Horses


Jack Easley

, DVM, MS, DAVDC (Equine), DABVP (EQ), Easley Equine Dentistry, Shelbyville, KY

Reviewed/Revised May 2019 | Modified Oct 2022

Problems of the mouth can involve the lips, teeth Dental Disorders of Horses Horses, like most other domestic large animals, are herbivores (plant eaters). If a horse’s teeth do not function well, it will be unable to eat properly and its overall health may be at risk... read more , tongue, or gums. These disorders can be caused by injury, infection, or internal diseases (for example, kidney failure).

Lip Lacerations

Wounds of the lips and cheeks are common in horses. They may be caused by a fall, a kick, the use of inappropriate bits or restraint devices or, more commonly, from the horse having its lips and sometimes jaw caught as it “plays” in its stall. Lip lacerations may be accompanied by a broken jaw or teeth and additional skin tearing (especially if the horse panics). Because of the large number of blood vessels in the lip region, healing is usually rapid after a veterinarian repairs it. However, once a wound has penetrated into the mouth, more extensive treatment is needed to avoid complications. Broken teeth or bones may also require additional treatment.

Paralysis of the Tongue

Paralysis of the tongue (called glossoplegia) is uncommon in horses. This condition may be seen in newborns because of the placement of obstetric snares used to aid in delivery. Such newborns need to be managed carefully to ensure that they are able to nurse. If not, your veterinarian may need to place a feeding tube to administer colostrum (the first milk). Intravenous fluids, anti-inflammatory drugs, and other treatments are often needed. If the condition persists for more than 10 days after birth, the likelihood of regaining normal function of the tongue is uncertain. Inflammatory diseases and trauma can also cause temporary paralysis of the tongue, as can conditions such as strangles, upper respiratory infections, meningitis, botulism, encephalomyelitis, or brain abscesses. Occasionally, horses undergoing long dental procedures can develop temporary paralysis of the tongue. The likelihood that the paralysis will resolve depends on its cause and the horse’s response to treatment.

Oral Tumors

Tumors of the mouth and lips other than viral papillomas (see Papillar Stomatitis, below) are uncommon in young horses. In gray horses, malignant skin cancers (melanomas) may develop near the corners of the mouth and cause hard, thickened, tumorous areas that may not be detected until they are well advanced. Oral and lip melanomas may be completely or partially removed by a surgical laser, or treatment with prescription medication.

Equine sarcoids are another type of tumor that can affect the mouth and lips. After removal with a surgical laser, the area is often treated with a chemotherapy drug. Alternatively, the tumors can be surgically frozen (cryotherapy).

Squamous cell carcinoma is a locally spreading tumor of the mouth and lips and can be difficult to treat. Treatment often involves surgical removal followed by surgical laser and the administration of a chemotherapy drug in the area. Regardless of treatment, the outlook for oral squamous cell carcinoma is uncertain to poor.

Slaframine Poisoning

Slaframine poisoning can occur when horses eat forages, particularly clovers, that are infected with the fungus Rhizoctonia leguminicola. The fungus produces the toxin slaframine. There are no abnormalities inside the mouth, and the only sign is profuse drooling. Removal of infected forage from the diet brings on rapid recovery. Most horses recover fully.

Inflammation of the Mouth (Stomatitis)

Inflammation of the mouth (stomatitis) has many possible causes. Trauma to the mouth or contact with chemical irritants (for example, horses that lick at their legs after having been blistered) may result in short-term inflammation. Traumatic injury from the ingestion of the sharp awns of barley, foxtail, porcupine grass, and spear grass, as well as feeding on plants infested with hairy caterpillars, will result in severe stomatitis in horses. Some infectious diseases (such as vesicular stomatitis Vesicular Stomatitis in Horses Vesicular stomatitis is caused by a virus and affects horses, cattle, and pigs. It also rarely affects sheep, goats, and llamas. The virus can be transmitted to humans and may cause flu-like... read more ) also cause inflammation of the mouth.

Common signs of stomatitis include:

  • frothy drooling

  • reluctance to eat

  • difficulty swallowing

  • resistance to examination of the mouth

The veterinarian will examine the horse’s mouth (usually with the animal under sedation) to allow removal of any embedded foreign matter, such as grass awns. If the cause is ingestion of foreign material, changing the quality and quantity of the hay or removing the horse from a pasture with grass awns may allow recovery.

It is important to have a veterinarian diagnose the cause of the inflammation, if possible, because a number of serious diseases can cause stomatitis. Other illnesses with similar signs include actinobacillosis and vesicular stomatitis.

Papillar Stomatitis

Viral papillomas (warts) are found around the lips and mouths of young animals. These lesions usually improve on their own. However, in some cases, they may grow together to form masses around the muzzles of young horses. If this is undesirable for cosmetic reasons, the papillomas can be treated by a veterinarian using liquid nitrogen to burn them off, surgical removal, or other treatments.

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