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Placenta: placentitis



  • 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 were Streptococcus zooepidemicus Streptococcus spp Placenta: placentitis - bacterial, Leptospira spp Leptospira interrogans, Escherichia coli Escherichia coli, a nocardioform actinomycete, fungi, Pseudomonas aeruginosa Pseudomonas aeruginosa, S. equisimilis, Enterobacter agglomerans, Klebsiella pneumoniae Klebsiella pneumoniae and alpha-hemolytic Streptococcus 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 of Leptospira spp cause placentitis via the ascending route. Leptospira spp placentitis lesions are due to hematogenous infection.
  • The route of infection of the nocardioform organism is unknown. Nocardioform placentitis Placenta: nocardioform placentitis 01 - pathologyPlacenta: 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 names Crossiella and Amycolatopsis.
  • 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 Vulva: 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 Female: reproductive cycle - normal: 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 Reproduction: 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 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.
  • Leptospira spp 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.
  • El-Sheikh Ali H, Legacki E L et al (2019) Equine placentitis is associated with a downregulation in myometrial progestin signalling. Biol Reprod 101 (1), 162-176 VetMedResource.
  • Wynn M A A, Ball B A et al (2018) Changes in maternal pregnane concentrations in mares with experimentally-induced, ascending placentitis. Theriogenology 122, 130-136 PubMed.
  • Canisso I F, Ball  BA et al (2017) Changes in maternal androgens and oestrogens in mares with experimentally-induced ascending placentitis. Equine Vet J 49 (2), 244-249 PubMed.
  • Canisso I F, Ball B A et al (2014) Serum amyloid A and haptoglobin concentrations are increased in plasma of mares with ascending placentitis in the absence of changes in peripheral leukocyte counts or fibrinogen concentration. Am J Reprod Immunol 72 (4), 376-385 PubMed.
  • Crabtree J (2012) Peripartum problems in mares. 1. Prepartum problems. In Pract 34 (7), 400-410 VetMedResource.
  • Christensen B W et al (2006) Nocardioform placentitis with isolation of Amycolatopsis spp in a Florida-bred mare. JAVMA 228 (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  et al (2004) First case of equine nocardioform placentitis caused by Crossiella equi in Europe. Vet Rec730-731 PubMed.
  • Bolin D C, Donahue J M, Vickers M L et al (2004) Equine abortion and premature birth associated with Cellulosimicrobium cellulans infection. J Vet Diag Invest 16, 333-336 PubMed.
  • Labeda D P, Donahue J M, Williams N M (2003) Amycolatopsis kentuckyensis sp nov, Amycolatopsis lexingtonensis sp nov, and Amycolatopsis pretoriensis sp nov, isolated from equine placentas. Int J Sys Evol Microbiol 53, 1601-1605 PubMed.
  • Cohen N D, Carey V J, Donahue J G et al (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 et al (2003) Encephalitozoon cuniculi placentitis and abortion in a Quarterhorse mare. J Vet Diag Invest 15, 57-59 PubMed.
  • Donahue J M, Williams N M, Sells S F & Labeda D P (2002) Crossiella equi sp nov, isolated from equine placentas. Int J Sys Evol Microbiol 52, 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. Pferdeheilkunde1 7 (6), 583-588 VetMedResource.
  • Donahue J M & Williams N M (2000) Emergent causes of placentitis and abortion. Vet Clin North Am Eq Pract 16 (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. JAVMA 216 (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), 7-11 Oxford Academic
  • Hong C B, Donahue J M, Giles Jr R et 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 et 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 et al (1993) Adenomatous hyperplasia of equine allantoic epithelium. Vet Pathol 30, 171-175 PubMed.
  • Hong C B, Donahue J M, Giles Jr R et 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 Pathol 25, 387-389 PubMed.
  • Prickett M E (1970) Abortion and placental lesions in the mare. JAVMA 157 (11), 1465-1470 PubMed.

Other sources of information

  • Waldridge B M & Pugh D G (2005) Equine Placentitis. Comp Cont 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, USA.

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