Equis ISSN 2398-2977

Vulva: conformation

Contributor(s): Philippa O'Brien, Christopher Phillips


  • Cause: various factors, such as natural conformation, aging, weight loss, perineal tumors or vulval injury during parturition can lead to abnormal vulval conformation in the mare. A poor vulval seal allows aspiration of air and comtaminants into the caudal reproductive tract, which may lead to ascending infection and endometritis.
  • Signs: external angulation of the vulva; recurrent endometritis; reduced fertility; aspiration of air during exercise.
  • Diagnosis: physical inspection of vulva; vaginal examination; endometrial cytology.
  • Treatment: Caslick's vulvoplasty; occasionally perineal reconstruction surgery.
  • Prognosis: good, if other causes of subfertility are not contributory.



  • Disruption of the vulvar seal due to conformation, previous injury or neoplasia.

Predisposing factors

  • Pluriparous mare.
  • Previous Caslick procedure.
  • Low body fat or loss of body condition.
  • Predisposing pelvic conformation with high-set tail and flat croup.
  • Perineal or labial injury during parturition.
  • Neoplasia such as perineal melanoma.


  • The vulvar labia should meet evenly from dorsal to ventral commisure, providing an airtight mucosal seal to protect the mare's reproductive tract from contamination from air and fecal matter.
  • Angulation of the vulva off the vertical allows increased contact with fecal material and more potential for vaginal contamination.
  • Two thirds of the vulva should be below the ischium.
  • Internally, the vestibulovaginal seal and the cervix from the second and third barriers against contamination of the uterus.
  • Deficiency in any of these seals will have implications for the mare's reproductive efficiency.
  • Aspiration of air through the vulva causes an inflammatory response and can predispose to bacterial infection.
  • Chronic inflammation of the endometrium can result in uterine fluid accumulation and prostaglandin release, shortening the luteal phase and resulting in reduced fertility.
  • A poor vulvar mucosal seal allows aspiration of air, bacteria and fecal material into the vagina.
  • Pneumovagina may lead to pneumouterus and an increase in inflammatory cells within the uterus, especially eosinophils.
  • Constant vaginal contamination results in uterine infection and endometritis, resulting in a hostile uterine environment and a subsequent reduction in fertility.


  • Depends on cause of poor vulval conformation; many mares will have good vulval conformation when they are young, with gradual decline over time and after numerous pregnancies.
  • Can be short if the cause is related to trauma.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Slusher S H, Freeman K P & Roszel J F (1984) Eosinophils in equine uterine cytology and histology specimens. JAVMA 184 (6), 665-670 PubMed.
  • Pascoe R R (1979) Observations on the length and angle of declination of the vulva and its relation to fertility in the mare. J Reprod Fertil Suppl (27), 299 PubMed
  • Caslick E A (1937) The vulva and vulvovaginal orifice and its relation to genital health of the Thoroughbred mare. Cornell Vet 27, 178-187 VetMedResource.

Other sources of information

  • Dascanio J J (2011) External Reproductive Anatomy. In: Equine Reproduction. Eds: McKinnon A O, Squires E L, Vaala W E & Varner D D. pp 1577-1581.
  • Pascoe R R (2007) Vulvar Conformation. In: Current Therapy in Equine Reproduction. Eds: Samper J C, Pycock J F & McKinnon A O. pp 140-145. 
  • Gadd J D (1975) The relationship of bacterial cultures, microscopic smear examination and medical treatment to surgical correction of barren mares. In: Proc Am Assoc Eq Pract. pp 362.