Equis ISSN 2398-2977

Placenta: placentitis

Contributor(s): Bradford G Bentz, Charles C Broaddus, Reed G Holyoak


  • Cause: bacterial or fungal infection of the placenta, route of infection may be ascending or hematogenous in origin.
  • Signs: vaginal discharge, premature udder development; subsequent abortions or weak foals.
  • Diagnosis: culture discharge, utero-placental assessment via ultrasound, gross placental evaluation, histopathology.
  • Treatment: antibiotics, anti-inflammatories, tocolytics. 
  • Prognosis: guarded.



  • Of 954 placentas submitted to the University of Kentucky Livestock Disease Diagnostic Center (USA) over a two year period, 236 had placentitis.
  • Only bacteria and fungi were isolated from the cases of placentitis: neither equine herpesvirus nor equine viral arteritis virus were isolated from any cases of placentitis.
  • In descending order of prevalence, the most commonly encountered pathogens associated with equine placentitis wereStreptococcus zooepidemicus  Streptococcus spp      Placenta: placentitis - bacterial  ,Leptospiraspp,Escherichia coli  Escherichia coli  , a nocardioform actinomycete, fungi,Pseudomonas aeruginosa  Pseudomonas aeruginosa  ,S. equisimilis,Enterobacter agglomerans,Klebsiella pneumoniae  Klebsiella pneumoniae  and alpha-hemolyticStreptococcus  Streptococcus spp  .
  • Infectious agents may reach the placenta by either the ascending caudal reproductive tract route or the hematogenous route. 
  • All of the above pathogens with the exception ofLeptospiraspp cause placentitis via the ascending route. Leptospiraspp placentitis lesions are due to hematogenous infection.
  • The route of infection of  the nocardioform organism is unknown.  Nocardioform placentitis   Placenta: nocardioform placentitis 01 - pathology    Placenta: nocardioform placentitis 02 - pathology   is a specific type of placentitis that is characterized by a solitary lesion at the cranial body/base of the horns that is covered with a brownish-tan mucoid material and culture of gram-positive filamentous branching bacteria. Several of the nocardioform isolates (formerly unclassified bacteria) have been classified and published with the namesCrossiellaandAmycolatopsis.
  • Mare reproductive loss syndrome (MRLS)   Reproduction: mare reproductive loss syndrome  may be associated with placentitis. One study identified placentitis or funisitis in 44% of MRLS cases, while another study found that about 10% of the cases of MRLS exhibited placentitis.

Predisposing factors

  • Body conformation: poor perineal conformation predisposes the mare to ascending reproductive tract infections by compromising the vulvar and vestibular seal.
  • Body condition Body condition scoring: mares with a poor body score condition are more likely to have poor perineal conformation, and thus more likely to develop placentitis.
  • Breed: Thoroughbred   Thoroughbred   mares are more susceptible to placentitis, due to their perineal conformation.
  • Season: the elevated levels of estrogen found in the lush forage of spring time pastures may cause cervical dilation and subsequent ascending cervical infection and placentitis.
  • Age: older, multiparous mares (particularly those with a history of dystocia and resulting perineal conformation changes) are at an increased chance of developing placentitis.
  • Environment: mares should not be allowed to come into contact with urine or urine contaminated feed, water or bedding from leptospirosis host species (wildlife, rodents or cattle).


  • Placentitis due to ascending cervical infections (of either bacterial or fungal origin) is characterized by infection in the cervical star area that extends a variable distance along the body of the placenta.
  • The lesions exhibit necrosis of chorionic villi, exudative material on the chorion, and infiltration of mononuclear inflammatory cells throughout the chorioallantoic membrane.
  • This disruption of the chorion causes a loss of placental function and subsequent fetal death or premature delivery.
  • Nocardioform actinomycetes induce a characteristic chronic placentitis and late-term abortions.  The lesion is frequently located at the base of the uterine horn, where the affected area is usually thickened and the chorionic surface is covered with brown, sticky, mucoid material.  This loss of functional placental surface area causes weak or stillborn foals.
  • Leptospiraspp may induce acute to chronic diffuse placentitis (usually between 6 and 9 months of gestation), although infection more commonly results in direct fetal death without placentitis. 
  • When placentitis is present, infection results in disruption of the interdigitation of the chorion with the endometrium and the subsequent loss of placental function.


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Further Reading


Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Crabtree J (2012)Peripartum problems in mares. 1. Prepartum problems.In Pract34(7), 400-410 VetMedResource.
  • Christensen B Wet al(2006)Nocardioform placentitis with isolation ofAmycolatopsisspp in a Florida-bred mare.JAVMA228(8), 1234-1239 PubMed.
  • Macpherson M L (2005)Treatment strategies for mares with placentitis. Theriogenology 64, 528-534 PubMed.
  • Cattoli G, Vascellari M, Corro M, Capua I, Mutinelli F, Sells S Fet al(2004)First case of equine nocardioform placentitis caused byCrossiella equiin Europe. Vet Rec730-731 PubMed.
  • Bolin D C, Donahue J M, Vickers M L, Giles R C, Harrison L, Jackson Cet al(2004)Equine abortion and premature birth associated with Cellulosimicrobium cellulans infection.J Vet Diag Invest16, 333-336 PubMed.
  • Labeda D P, Donahue J M, Williams N M, Sells S F & Henton M M (2003)Amycolatopsis kentuckyensissp. nov.,Amycolatopsis lexingtonensissp. nov., andAmycolatopsis pretoriensissp. nov., isolated from equine placentas.Int J Sys Evol Microbiol53, 1601-1605 PubMed.
  • Cohen N D, Carey V J, Donahue J G, Seahorn J L & Harrison L R (2003)Descriptive epidemiology of late-term abortions associated with the mare reproductive loss syndrome in central Kentucky.J Vet Diag Invest 15, 295-297 PubMed.
  • Patterson-Kane J C, Caplazi P, Rurangirwa F, Tramontin R R & Wolfsdorf K (2003) Encephalitozoon cuniculi placentitis and abortion in a Quarterhorse mare.J Vet Diag Invest15, 57-59 PubMed.
  • Donahue J M, Williams N M, Sells S F & Labeda D P (2002)Crossiella equisp. nov., isolated from equine placentas.Int J Sys Evol Microbiol52, 2169-2173 PubMed.
  • Palmer E, Chavette-Palmer P & Duchamp G (2002) Lack of effect of clenbuterol for delaying parturition in late pregnant mares. Theriogenology 58, 797-799 VetMedResource.
  • Allen W R & Stewart F (2001)Equine placentationRepro Fert Development 13, 623-634 PubMed.
  • Troedsson M H T (2001)Ultrasonographic evaluation of the equine placenta.Pferdeheilkunde 17(6), 583-588 VetMedResource.
  • Donahue J M & Williams N M (2000) Emergent causes of placentitis and abortion.Vet Clin North Am Eq Pract16(3), 443-456 PubMed.
  • Wolfsdorf K E, Williams N M & Donahue J M (2000)Theriogenology question of the month. Bacterial placentitis attributable to a gram-positive filamentous branching bacillus organism.JAVMA216(12), 1915-1916 PubMed.
  • Zent W W, Williams N M & Donahue J M (1999) Placentitis in central Kentucky broodmares.Pferdeheilkunde 15(6), 630-632 VetMedResource.
  • Card C E & Wood M R (1995)Effects of acute administration of clenbuterol on uterine tone and equine fetal and maternal heart rates. Biol Repro Mono 1(1), 7-11 Oxford Academic
  • Hong C B, Donahue J M, Giles Jr R, Petrites-Murphy M B, Poonacha K B, Roberts A Wet al(1993)Etiology and pathology of equine placentitis.J Vet Diagn Invest 5, 56-63 PubMed.
  • Giles R C, Donahue J G, Hong C B, Tuttle P A, Petrites-Murphy M B, Poonacha K Bet al(1993)Causes of abortion, stillbirth, and perinatal death in horses: 3,527 cases (1986-1991).JAVMA 203, 1170-1175 PubMed.
  • Hong C B, Donahue J M, Giles Jr R, Petrites-Murphy M B, Poonacha K B, Tramontin R Ret al(1993)Adenomatous hyperplasia of equine allantoic epithelium.Vet Pathol30, 171-175 PubMed.
  • Hong C B, Donahue J M, Giles Jr R, Petrites-Murphy M B, Poonacha K B, Roberts A Wet al(1993)Equine abortion and stillbirth in central Kentucky during 1988 and 1989 foaling seasons.J Vet Diag Invest 5, 560-566 PubMed.
  • McEntee M, Brown T & McEntee K (1988)Adenomatous dysplasia of the equine allantois.Vet Pathol25, 387-389 PubMed.
  • Prickett M E (1970) Abortion and placental lesions in the mare.JAVMA157(11), 1465-1470 PubMed.

Other sources of information

  • Waldridge B M & Pugh D G (2005) Equine Placentitis.Compendium Contin Educ Pract Vet.pp 573-575.
  • LeBlanc M M, Macpherson M & Sheerin P (2004) Ascending placentitis: what we know about pathophysiology, diagnosis, and treatment.In:Proc 50th Annual Convention of the AAEP. Denver, Colorado, USA.
  • Neil Williams - Personal Communication.