Vagina: pneumovagina in Horses (Equis) | Vetlexicon
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Vagina: pneumovagina

ISSN 2398-2977


  • Vulvar lips cease to act as a seal, therefore air +/- feces becomes aspirated into vagina → dilation of the vagina, and possibly uterus plus contamination with bacteria.
  • Cause: aging, vulval conformation, weight, trauma (especially multiple foalings +/- injuries).
  • Signs: vaginitis, endometritis, and infertility may result. Pneumovagina may occur only during estrus.
  • Diagnosis: predisposing external conformation of vulva, anus and perineum, vaginoscopy, cytology, bacteriology.
  • Treatment: surgery, especially Caslick's operation; address predisposing factors.
  • Prognosis: surgery will need to be repeated after each pregnancy. Possibly repaired at mating, require episiotomy prior to foaling. Good to guarded.
  • See also reproductive management of the mare Reproduction: management - female.

Presenting signs

  • Poor vulvar conformation Vulva: conformation 01 - broodmare. Two types have been described:
  • Long length of vulva above pelvic brim. Dorsal commissure of vulva drawn cranially with advancing age Vulva: 80 degree vulval conformation.
  • Dished vulvar conformation Vulva: conformation 02 - after Pouret and Caslick operation Vulva: poor conformation 02 (sunken anus with cranially tipped vulva - dorsal vulvar commissure >5 cm above brim of pelvis).
  • Vaginitis.
  • Endometritis.
  • Subfertility.
  • Poor body condition (often correctable if improvement in body condition).
  • Infertility.
  • Incompetent vulvo-vaginal sphincter due to stretching or tearing.
  • 'Windsucking' through the vulva may be audible when the mare urinates, or when she moves.

Geographic incidence

  • Worldwide.

Age predisposition

  • Aged (multiparous).
  • Adult.

Breed/Species predisposition

  • Affects almost every breed.

Cost considerations

  • Decreased fertility with repeated diagnostic/reproductive system/examinations.
  • Requires repeated surgery, both to re-do the anatomical defect, and to reverse that correction before foaling (Caslick procedure Vulva: Caslick operation).



  • Poor vulvar conformation.

Predisposing factors


  • Advancing age.
  • Poor body condition.
  • Multiparity.
  • Trauma to vulva, vestibule or perineal body during foaling, and to a lesser extent during mating.
  • External trauma to vulvar labia.
  • Bad conformation, eg flat croup, high tail head (level with the sacroiliac joint); sunken anus.


  • There are normally three levels of seal between the external environment and the uterus: the vulval lips, the vestibular sphincter (also known as the vestibulovaginal fold), and the cervix.
  • When vulvar lips cease to act as a seal between → air, bacteria and other contaminated material (feces) enters the vagina → vaginitis → debris and air get drawn through the open cervix during estrus into the uterus → endometritis → infertility.
  • Poor vulvar conformation, eg vulva high in relation to pelvic brim and/or cranially sloping vulva, combined with other predisposing factors, especially age and multiparity → vulval lips cease to act as a seal → air aspirated into vagina and/or fecal contamination of vagina → vaginitis Vagina: bacterial infection → ascending infection → endometritis Uterus: endometritis - bacterial → infertility or subfertility.
  • Some cases develop urinary tract infection (very rare). Urovagina may develop in some cases, particularly when vulvar lips sutured ventrally too low so as to obstruct exit of urine.
  • Mares in poor body condition → thin-lipped, toneless muscled vulva.
  • Overweight mares → labial lips become inverted, disrupting seal.
  • Vulvar defect is often more apparent during estrus, when perineum more relaxed or when sedated and tail elevated for examination.
  • Repeated trauma during foaling, eg repeated stretching or laceration of vulva, vestibule or perineal body Perineum: trauma → disrupt vulvar barrier by damaging underlying musculature.
  • Older multiparous mares → abdominal enlargement and stretching of mesometriu → splanchnoptosis → anus pulled cranially → distortion of perineum → vulva becomes more horizontal.
  • Fit underweight mares or some maiden mares may have the vulval lips drawn forwards and decreased substance to labia with weak musculature.


  • Chronic; conformational defect usually increases with age.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Inoue Yu & Sekiguchi M (2017) Vestibuloplasty for persistent pneumovagina in mares. J Equine Vet Sci 48, 9-14 VetMedResource.
  • Pouret E J (1982) Surgical technique for the correction of pneumo- and urovagina. Equine Vet J 14, 249-250 PubMed.
  • Pascoe R R (1979) Observations on the length and the 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 the vulvo-vaginal orifice and its relation to genital health of the Thoroughbred mare. Cornell Vet 27, 178-187 VetMedResource.

Other sources of information

  • McKinnon A O & Jalim S L (2011) Surgery of the Caudal Reproductive Tract. In: Equine Reproduction. 2nd edn. Eds: McKinnon A O, Squires E L, Vaala W E & Varner D D. Blackwell Publishing, UK. pp 2545-2558.
  • McKinnon A O & Vasey J R (2007) Selected Reproductive Surgery of the Mare. In: Current therapy in Equine Reproduction. Eds: Samper J C, Pycock J F & McKinnon A O. Saunders, USA. pp 146-153.