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Also Known As

Mammary gland inflammation


Mastitis is an inflammation of one or more quarters of the mammary gland in a mare and is usually caused by bacterial infection. Mastitis may also be caused by chemical or physical agents or, in some cases, by a tumor. While instances of the disease are rare, when it occurs it must be treated promptly.

Clinical signs vary with the severity of the condition, but usually the udder becomes warm, swollen, and painful. Diagnosis by a veterinarian is important, and the foal should be temporarily removed and fed by hand until diagnosis and treatment are completed.


  • Swollen, warm, painful udder
  • Consistency of milk may be watery, with cloudy flakes or strands, or it may appear curdled or bloody
  • Mare may refuse to allow foal to nurse or foal will be unable to get milk
  • Underside of abdomen may be swollen and warm to touch


Mastitis is most often caused by a bacterial infection, but also may be caused by chemical or physical agents or by a tumor. It usually occurs a few weeks after foaling. Laboratory examination of the milk will show bacteria, with staphylococci and streptococci being the most prevalent.


A clean environment is the best prevention for infectious diseases such as mastitis. Washing the mare's udder with a disinfectant solution periodically and keeping the stall mucked and equipment clean and in good condition will reduce harmful bacteria in the environment.


The foal should be stopped from nursing and fed by hand during treatment to relieve the condition. The udders should be emptied by hand to relieve pressure and for continued milk production.

Cold packs will help reduce swelling and the veterinarian will prescribe antibiotics pending results of the milk culture. Unless other factors are in play, such as a tumor, the infection will respond rapidly to treatment and the foal can return to the mare usually within a week.

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EquiMed Staff

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.