Problems of the mouth can involve the lips, teeth, 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. However, once a wound has penetrated into the mouth, more extensive treatment is needed to avoid complications.

Paralysis of the Tongue

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. Intravenous fluids and anti-inflammatory 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 slight. Inflammatory diseases and trauma can also cause temporary paralysis of the tongue, as can conditions such as upper respiratory infections, meningitis, botulism, encephalomyelitis, or brain abscesses.

Oral Tumors

Tumors of the mouth and lips other than viral papillomas (see Digestive Disorders of Horses: Papillar Stomatitis) 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. Treatment of oral and lip melanomas in the horse is often unsuccessful, although treatment with prescription medication may provide relief.

Slaframine Poisoning

Slaframine poisoning (see Poisoning: Slaframine Poisoning) can occur when horses eat forages, particularly clovers, that are infected with the fungus Rhizoctonia leguminicola. The fungus produces the toxic alkaloid slaframine. There are no abnormalities inside the mouth, and the only sign that may help in diagnosis 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 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 also cause inflammation of the mouth.

Frothy drooling, reluctance to eat, and resistance to examination of the mouth are the common signs of stomatitis. 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 may allow recovery.

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

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, vaccines, or a combination of treatments.

Last full review/revision July 2011 by Peter D. Constable, BVSc (Hons), MS, PhD, DACVIM; Gordon J. Baker, BVSc, PhD, MRCVS, DACVS; Joseph A. DiPietro, DVM, MS; Walter Ingwersen, DVM, DVSc, DACVIM; John E. Madigan, DVM, MS; James N. Moore, DVM, PhD; Michael J. Murray, DVM, MS; Sofie Muylle, DVM, PhD; Stanley I. Rubin, DVM, MS, DACVIM; Susan D. Semrad, VMD, PhD, DACVIM; Josie L. Traub-Dargatz, DVM, MS, DACVIM