Stomatitis in Donkeys: Inflammation of the Mouth and What Causes It

Stomatitis is a general term for inflammation of the tissues inside the mouth. In donkeys, that can include the lips, gums, tongue, cheeks, and roof of the mouth. The problem is not one single disease. Instead, it is a clinical finding that can happen for several reasons, including irritation, injury, dental disease, infection, or exposure to caustic plants or chemicals.

Mild cases may cause only redness and tenderness. More serious cases can lead to ulcers, erosions, swelling, drooling, foul breath, and reluctance to eat. Because donkeys often hide discomfort, a pet parent may first notice slower eating, quidding, weight loss, or feed packed in the cheeks rather than obvious mouth pain.

One important cause your vet may consider is vesicular stomatitis, a reportable viral disease that affects horses, donkeys, mules, cattle, swine, and camelids. It can cause painful blisters and ulcers in and around the mouth, along with excessive salivation and difficulty eating. That is one reason any donkey with sudden oral sores should be examined promptly.

Stomatitis in donkeys has many possible causes, so your vet will usually think in categories rather than jumping to one answer. Mechanical and dental causes are common starting points. Sharp enamel points, fractured teeth, periodontal disease, feed impaction, foreign material, or rough hay stems can all traumatize the mouth and set up inflammation. Oral pain may also be worse if there is underlying dental disease that makes chewing abnormal.

Chemical or plant irritation is another possibility. Caustic drenches, irritating topical products, accidental exposure to chemicals, or abrasive forage can inflame delicate oral tissues. Some donkeys also develop mouth irritation after chewing on rough plants, contaminated feed, or foreign objects in the environment.

Infectious causes matter too. Vesicular stomatitis is especially important because it can affect donkeys and causes painful vesicles that quickly ulcerate. Typical signs include drooling, oral ulcers, crusting around the muzzle, trouble prehending and chewing feed, and sometimes lesions at the coronary band with lameness. Because it can resemble other serious vesicular diseases in some species and is reportable, suspected cases need veterinary evaluation right away.

Less common causes can include severe periodontal disease, oral masses, deeper tooth-root infection, or systemic illness that makes the mouth more vulnerable to ulceration. In older equids, advanced dental and periodontal problems can create chronic inflammation, feed packing, drainage, and pain that look like primary mouth disease when the teeth are actually the driver.

Diagnosis starts with a careful history and physical exam. Your vet will ask when the signs started, what your donkey has been eating, whether there has been any new pasture, hay, chemicals, tack, or herd exposure, and whether other animals are affected. Because donkeys may resist a painful oral exam, sedation is often needed for a safe and thorough look inside the mouth.

A complete oral exam may include a speculum exam, inspection of the tongue, gums, cheeks, palate, and lips, and evaluation of the teeth for sharp points, fractures, periodontal pockets, feed trapping, or other painful lesions. If your vet suspects deeper dental disease or a more complex oral problem, dental radiographs or referral-level imaging may be recommended.

If the lesions look vesicular or ulcerative in a pattern that raises concern for infectious disease, your vet may advise immediate isolation and regulatory testing. Definitive diagnosis of vesicular stomatitis requires laboratory testing through approved channels, and suspected cases are reported to animal health officials in the U.S. Depending on the case, your vet may also recommend bloodwork, culture, biopsy, or targeted testing to rule out trauma, infection, or oral masses.

Prevention starts with routine oral health care. Regular dental exams help your vet catch sharp enamel points, fractured teeth, periodontal disease, and feed trapping before they lead to painful mouth inflammation. Many equids need sedation for a complete and safe oral exam, and that can make a big difference in finding problems early.

Feed and environment also matter. Offer clean forage, avoid moldy or contaminated feed, and check hay for coarse stems, awns, or foreign material that could injure the mouth. Keep caustic chemicals, irritating topical products, and unsafe plants out of reach. If your donkey uses tack or equipment that contacts the mouth, make sure fit and condition are appropriate and that there are no rough or damaged surfaces.

Good biosecurity is important when oral lesions appear suddenly, especially during vesicular stomatitis activity in the U.S. Reduce insect exposure, use fly control, avoid sharing equipment between animals with mouth lesions, and isolate any donkey with suspicious blisters, ulcers, or heavy drooling until your vet advises otherwise. Early veterinary attention is one of the best prevention tools because it can stop a mild mouth problem from becoming a painful feeding crisis.