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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Inflammation of the placenta. Single most important cause of late-term abortion, stillbirth, and premature delivery in the mare.

Pathophysiology!!navigator!!

  • An infectious agent (e.g. bacterial, viral, mycotic) invades the placenta, leading to an inflammatory response
  • Typically, initial location is in the area of the cervical star, when cause is ascending
  • Placental detachment and thickening—may be localized or widespread
  • Uterine motility is altered in response to local inflammation
  • Modes of entry
    • Ascending via cervix (most common)
    • Hematogenous, as part of systemic illness
    • Inoculation
    • Recrudescence of preexisting focus of infection

Systems Affected!!navigator!!

Reproductive

Genetics!!navigator!!

N/A

Incidence/Prevalence!!navigator!!

Common if any of modes of entry are in play or if vulvar conformation is less than ideal (ascending route of infection).

Signalment!!navigator!!

Pregnant mare typically during late gestation.

Signs!!navigator!!

  • Vulvar discharge—purulent; hemorrhagic
  • Cervical incompetence—discharge; inflammation
  • Mammary—swelling; discharge; prepartum lactation
  • Relaxation of pelvic musculature—vulva; sacrosciatic ligament
  • Restlessness; premonitory foaling behavior
  • Placenta—thickening; edema; increased weight; discoloration; discharge; adenomatous hyperplasia; plaque formation, especially centered on cervical star

Causes!!navigator!!

Bacterial

  • Throughout gestation
  • 2 presentations
    • Acute, focal or diffuse
    • Chronic, focal or extensive
  • Acute, focal or diffuse
    • Neutrophil infiltration
    • Necrosis of chorionic villi
    • Primarily early to mid-gestation
  • Chronic, focal or extensive
    • Centered around area of cervical star
    • Eosinophilic chorionic material
    • Necrosis of villi
    • Adenomatous hyperplasia
    • Mononuclear cell infiltration
    • Primarily mid- to late gestation
  • Common pathogens
    • Streptococcus equi ssp. zooepidemicus
    • Streptococcus equisimilis
    • Escherichia coli
    • Pseudomonas aeruginosa
    • Klebsiella pneumoniae
  • Leptospira spp.
    • Diffuse, spirochete invasion
    • Hematogenous spread only
  • Crossiella equi
    • Other actinomycete species also occur; base of horns and body
    • Gram-positive filamentous bacillus infiltration
    • Chronic nature

Viral

  • Equine viral arteritis
    • Thickening of allantochorion attributable to a longer incubation time before abortion
    • Compare/contrast with equine herpesvirus 1, with which there are either no or nonspecific placental changes

Fungal

  • Usually 300 days of gestation or later
  • Aspergillus spp.—chronic, focal placentitis at cervical star similar to chronic bacterial cases
  • Candida spp.—diffuse; necrotizing; proliferative
  • Histoplasma spp.—multifocal; granulomatous

Anatomic

  • Cervical incompetence—laceration; age-induced degeneration. Bacterial invasion resulting in placentitis
  • Vulvar and vestibular incompetence—aspiration of external irritants and debris
  • Production of prostaglandin F2α by endotoxin release, leading to cervical relaxation

Risk Factors!!navigator!!

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

  • Impending parturition
  • Fescue toxicosis—placental edema; delayed parturition; decreased lactation
  • Other causes of vulvar discharge
    • Vaginitis (speculum examination to assess cervical integrity/discharge)
    • Endometritis
    • Pyometra
    • Metritis
    • Vaginal varicosities
  • Uterine trauma or hemorrhage
  • Urinary tract infection
  • Urine pooling
  • Uterine or vaginal neoplasia
  • Other causes of lactation—endocrine, seasonal
  • Other causes of relaxation—impending parturition

CBC/Biochemistry/Urinalysis!!navigator!!

  • CBC may remain normal even with significant placental pathology
  • Leukocytosis with neutrophilia
  • Hyperfibrinogenemia
  • Biochemistry, usually normal
  • Urinalysis, normal

Other Laboratory Tests!!navigator!!

Mares with placentitis have been demonstrated experimentally to have increased concentrations of either P5 and/or progesterone P4 along with a number of metabolites. This suggests increased fetal production of P5 and/or P4 and increased uteroplacental metabolism in response to chronic stress.

Imaging!!navigator!!

Transrectal US

  • Marked increase in the CTUP measured by US, especially in the cervical region of the uteroplacental unit
  • Good indicator of ascending placentitis
  • Normal ranges for the area immediately cranial to the cervix have been established from 4 months of gestation to term in normal pregnant mares using transrectal US
  • Mean CTUP is:
    • Approximately 4 mm between the fourth and ninth months of pregnancy
    • After which time it increases 1.5–2 mm each month until the end of gestation
    • Alternately, CTUP of up to 7 mm prior to day 300 has been considered normal
    • Obtain measurements from a consistent area on the ventral body of the uteroplacental unit
  • This is aided by including regional vein in field of view
  • Edema at cervical pole common in final month of gestation

Transabdominal US

  • Range of CTUP 12.6 ± 0.33 mm
  • Avoid areas of compression by fetus
  • Observe for anechoic or particulate fluid between uterus and allantochorion
  • Ensure vascular structures are not erroneously identified
  • Areas of placental folding or detachment from endometrium
  • Allantoic fluid debris

Other Diagnostic Procedures!!navigator!!

  • Microbial culture of discharge from cervix
  • Cytology—neutrophils, with or without intracellular bacteria; fungal elements

Pathologic Findings!!navigator!!

Examination of the allantochorion.

Gross

  • Thickened; discolored
  • Bright red chorion becomes gray/brown, with plaques; avillous areas; exudative
  • Examine umbilical cord, fetus for inflammatory changes

Histopathologic

  • Necessary to differentiate bacterial from mycotic
  • Inflammatory infiltrate, fibrosis, thrombosis, edema; causative agent—bacteria or fungal elements

Microbiologic Examination

Bacterial/fungal/viral isolation.

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Remove inciting cause—control infectious agent (bacterial, fungal)
  • Control placental, endometrial inflammation, e.g. Caslick's vulvoplasty, progesterone supplementation
  • Clinical trials indicate that long-term treatment improves pregnancy outcome
  • Maintain fetoplacental function
  • Prevent fetal expulsion
    • If mare carries to 300 days, chance of fetal survival increases
    • Stress of intrauterine environment accelerates fetal maturity
  • Maintain maternal health

Nursing Care!!navigator!!

Minimize maternal and fetal stress.

Activity!!navigator!!

Stall rest the mare.

Diet!!navigator!!

N/A

Client Education!!navigator!!

Monitor subsequent pregnancies.

Surgical Considerations!!navigator!!

Repair of cervical and conformational defects, if present.

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

Antibiotics

  • Penicillin G; gentamicin
  • Trimethoprim–sulfa
  • Selection based on sensitivities of most likely pathogen

Anti-inflammatories

  • NSAIDs decrease endotoxin production
  • Decrease luteolytic potential
  • Decrease myometrial contractility
  • Decrease incidence of laminitis

Anticytokine Therapies

  • Pentoxifylline 8.5 mg/kg BID PO
  • Decreases production of inflammatory mediators
  • Has led to pregnancy maintenance in mouse endotoxemia model

Progestagen Supplementation

  • Altrenogest (Regumate) 0.044 mg/kg PO once daily for routine administration may be given at 0.088 mg/kg daily for the last 20 ± 5 days of pregnancy; helps to decrease uterine excitability
  • Maintains production of histiotroph, fetal nutrition
  • Aids cervical competency

Contraindications!!navigator!!

If fetal death occurs:

  • Discontinue progestagens
  • Allow abortion to occur
  • Avoid in utero fetal decomposition
  • Continue antimicrobial and anti-inflammatory treatment of mare
  • Monitor for laminitic changes

Precautions!!navigator!!

N/A

Possible Interactions!!navigator!!

N/A

Alternative Drugs!!navigator!!

N/A

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Mare

  • Transrectal US of cervix and caudal uterine body to evaluate thickness and detachment of placenta
  • Transabdominal US to monitor placental integrity, fetal viability
  • Attend parturition
    • Increased incidence of premature placental separation, and/or
    • Decreased likelihood of thickened allantochorion to rupture readily at cervical star during delivery
    • Either circumstance can lead to neonatal asphyxiation
  • Preterm mammary development (especially if >30 days before parturition)
  • Premature lactation—loss of colostral antibodies; potential failure of passive transfer of immunity
  • Placental examination—to ensure no retained fetal membranes
  • Diagnostic samples—microbiologic and histologic from placenta, fetus
  • Vaginal speculum examination to monitor cervix—closure, relaxation, and discharge
    • Use with caution
    • This procedure disrupts existing vulvar and vestibular barriers to ascending uterine infection

Neonate

  • Increased potential for sepsis
  • Increased potential for neurologic compromise
  • Possible intrauterine growth retardation
  • Prepartum lactation may have depleted colostral antibodies
  • Fetal ECG in late gestation (final trimester)

Prevention/Avoidance!!navigator!!

  • Breeding soundness examination of the mare when not pregnant; include examination of cervical competence
    • Best if in diestrus at time of examination
  • Prebreeding preparation of mare and stallion—hygiene
  • Keep environment and housing of pregnant mares as clean as possible

Possible Complications!!navigator!!

  • Abortion
  • Dystocia
  • Sick, weak neonate

Expected Course and Prognosis!!navigator!!

N/A

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Associated Conditions!!navigator!!

  • Premature placental separation
  • Laminitis
  • Fetal sepsis—bacterial; fungal
  • Neonatal sepsis and compromise

Age-Related Factors!!navigator!!

Endometrial health and cervical competence decline with age and increasing parity of mares.

Zoonotic Potential!!navigator!!

N/A

Pregnancy/Fertility/Breeding!!navigator!!

Abortion

Abbreviations!!navigator!!

  • CTUP = combined thickness of the uterus and placenta
  • NSAID = nonsteroidal anti-inflammatory drug
  • P4 = progesterone
  • P5 = pregnenolone
  • US = ultrasound, ultrasonography

Suggested Reading ⬆ ⬇

Bucca S, Fogarty U, Collins A, Small V. Assessment of feto-placental well-being in the mare from mid-gestation to term: transrectal and transabdominal ultrasonographic features. Theriogenology2005;64:542–557.

Macpherson ML. Treatment strategies for mares with placentitis. Theriogenology 2005;64:528–534.

Ousey JC, Houghton E, Grainger L, et al. Progestagen profiles during the last trimester of gestation in Thoroughbred mares with normal or compromised pregnancies. Theriogenology 2005;63:1844–1856.

Renaudin CD, Troedsson MH, Gillis CL, et al. Ultrasonographic evaluation of the equine placenta by transrectal and transabdominal approach in the normal pregnant mare. Theriogenology 1997;47:559–573.

Author(s) ⬆

Author: Peter R. Morresey

Consulting Editor: Carla L. Carleton