Merck Manual

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Pet Owner Version

Pyometra in Horses


Robert O. Gilbert

, BVSc, MMedVet, DACT, MRCVS, Reproductive Medicine, Department of Clinical Sciences, College of Veterinary Medicine, Cornell University

Reviewed/Revised Sep 2019 | Modified Oct 2022

Pyometra is an infection of the uterus characterized by the accumulation of large amounts of pus. This condition is often caused by an abnormal cervix or poor uterine clearance mechanisms. Infected mares may continue to cycle normally, or the cycle may be interrupted. Discharge from the genital tract (vagina) may be absent or intermittent and correspond to the periods of estrus.

Although pyometra causes the mare to be infertile, it rarely affects the general health and well-being of the mare. Your veterinarian will perform tests to distinguish between pregnancy and pyometra before prescribing any treatment. The condition may be managed by uterine lavage and the administration of drugs that will cause the uterus to contract and empty. However, in severe cases, treatment may require surgical removal of the uterus.

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