Fistulous Withers

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Also Known As

Saddle sore, Wither sinus inflammation


A fistula is an abnormal passage that leads from an infection within the horse's body to the outside of the body, in the case of fistulous withers, the outside of the horse's withers. Fistulous withers is a chronic inflammatory disease of the bursa, the sac-like container of lubricating fluid near the spine of the horse, caused by either infection, parasites, or physical factors.

Swelling of the withers, drainage of pus from an open lesion resulting from inflammation, and infection that spreads from the infected bursa to surrounding tissues are common characteristics of the disease.

Blunt trauma to the withers and infection of an open wound may also lead to the inflammation resulting in fistulous withers. Trauma may be caused by an ill fitting saddle or harness, but may also be caused by sharp contact with a fence, another horse, or from a gun shot wound.

Knowing whether or not trauma is involved aids in treatment decisions. A history of exposure to cattle that might test positive for Brucella abortus increases the chance that the lesion is linked to a Brucella abortus infection.

Brucella abortus can be spread from animals to humans who may become infected through skin abrasions, the mucous membranes, or indirect contact by ingestion or inhalation of the organism. When humans are infected, the disease is known as undulant fever.

Infected horses may not show symptoms for as long as two years after initial infection. A complete physical examination is necessary to diagnose the disease. Any serious injury or swelling at the withers needs prompt veterinary attention.


  • Swollen withers
  • Signs of fever and pain
  • Open drainage fistulas
  • Lameness
  • Systemic illness
  • Swelling at other areas


Causes of the disease may be the result of infectious, parasitic, or physical factors. Actinomyces bovis and Brucella abortus are the common organisms responsible for fistulous withers, blunt trauma to the withers caused by tack or sharp contact with a fence or another horse or object can lead to infection and inflammation resulting in fistulous withers. The hair-like parasite Onchocerca cervicalis has also been implicated in the early stages of the disease.


Prompt attention to any injuries to the withers area will help prevent infections that cause fistulous withers. In the case of B. abortus infection, the horse should be quarantined to prevent contact with other horses and humans. Discharges should be handled with caution. Horses should not be pastured in areas where infected cattle have been for at least three months after the cattle have been removed.


Treatment of fistulous withers is difficult because of the often deep-seated nature. Antibiotics are effective in early stages. Vaccination with Brucella vaccine may help to resolve the disease when it is determined that Brucella abortus is the cause of the disease.

If the condition becomes chronic, surgical removal of devitalized and infected tissue may be necessary for a permanent cure. In any case, a veterinarian should be consulted both as to the exact cause of the condition and the best treatment available.

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EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.