Equis ISSN 2398-2977

Uterus: pyometra

Contributor(s): David Dugdale, Jean Pierre Held, Graham Munroe, Sarah Stoneham, Madeleine L H Campbell


  • Pyometra is the accumulation of pus in the lumen of the uterus.
  • Cause: some interference with the usual process of fluid clearance from the uterus; a sequel to endometritis; cervicitis; cervical adhesions following previous dystocia; functional failure of the cervix to relax (so called 'fibrotic cervix'; persistent corpus luteum).
  • Signs: some cases show irregular estrous cycles; generally no systemic signs.
  • Diagnosis: culture of uterine fluid; endometrial biopsy, ultrasonography.
  • Treatment: mechanical evacuation; intrauterine antibiotics; ovariohysterectomy if unresolved.
  • Prognosis: worse if endometrial atrophy and/or anestrus.



Predisposing factors


  • Cervical or caudal uterine adhesions.
  • Trauma.
  • Cervicitis.
  • Functional closure of the cervix (so called 'fibrotic cervix'; persistent corpus luteum).
  • Uterine therapy with irritating agents.
  • Reduced endometrial resistance.
  • Hot, dry, dusty regions.
  • Some types of dystocia Reproduction: dystocia.


  • Accumulation of pus in uterine lumen due to interference with normal mechanisms of clearance of fluid from the uterus; may follow cervicitis or endometritis Uterus: endometritis - bacterial.
  • Persistence of a corpus luteum beyond its normal life span may be present.
  • Endometritis or cervicitis → caudal uterine or cervical adhesions → accumulation of purulent exudate and endometrial glandular secretions in uterus.
  • Some cases occur without occlusion of cervix; may result from dystocia or lowered endometrial resistance to disease and impaired uterine clearance.
  • Sometimes, but not always associated with, damage to endometrial epithelial tissue, endometrial inflammation and endometrial fibrosis.
  • Hot, dry, dusty areas → pyometra with extensive endometrial damage → severe fibrosis and glandular atrophy → inadequate endogenous uterine prostaglandin production and failure of luteolysis → persistent diestrus Female: prolonged diestrus. More often associated with Pseudomonas aeruginosa infection.
  • Colder, wetter areas → pyometra less common → less extensive endometrial damage; possibly endometrial glandular hyperplasia → recurrent inflammatory stimulus → premature prostaglandin release → luteolysis → short estrous cycles. More often associated with Streptococcus zooepidemicus and/or E. coli infection.
  • If uterine fluid is viscid, grayish, bacteriologically sterile, amorphous and eosinophilic → mucometra.


  • Usually chronic.


  • May be associated with increased incidence of Pseudomonas aeruginosa infection.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Arnold C E, Brinsko S P & Varner D D (2015) Cervical wedge resection for treatment of pyometra secondary to transluminal cervical adhesions in six mares. JAVMA 246 (12), 1354-1357 PubMed.
  • Woodford N S, Payne R J & McCluskie L K (2014) Laparoscopically-assisted ovariohysterectomy in three mares with pyometra. Equine Vet Educ 26 (2), 75-78 VetMedResource.
  • Casey R C (2006) Making sense of equine uterine infections: the many faces of physical clearance. Vet J 172 (3), 405-421 PubMed.
  • Rotting A K, Freeman D E, Doyle A J et al (2004) Total and partial ovariohysterectomy in seven mares. Equine Vet J 36 (1), 29-33 PubMed.
  • Hughes P J et al (1979) Pyometra in the mare. J Reprod Fertil Suppl 27, 321-329 PubMed.