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Basics ⬇

Outline

BASICS

Definition!!navigator!!

Fetal loss >40 days (term stillbirth may apply >300 days) due to noninfectious conditions.

Pathophysiology!!navigator!!

Approximately 85–95% of abortions are noninfectious in nature. Some of the specific causes of spontaneous, noninfectious equine abortions are as follows.

  • Twin pregnancies that persist >40 days, ≈70% end in abortion/stillbirth
  • Luteal insufficiency/early CL regression
    • Anecdotal—decreased levels of luteal progesterone at <80 days of gestation
  • Placental abnormalities
    • Umbilical cord torsion, as evidenced by vascular compromise, e.g. cord thrombus, can be associated with abortion
    • Torsion of the amnion
    • Long umbilical cord/cervical pole ischemia disorder
    • Confirmed body pregnancy
    • Placental separation
    • Villous atrophy, hypoplasia, or placental insufficiency (can also be associated with prolonged gestation)
    • Hydrops
    • Various placental abnormalities reported with foals resulting from SCNT
  • Fetal abnormalities
    • Developmental abnormalities, such as hydrocephalus or anencephaly
    • Fetal trauma
    • Chromosomal abnormalities
  • Maternal abnormalities
    • Concurrent maternal disease, such as PPID and EMS/IR
    • Trauma
    • Malnutrition/starvation; selenium deficiency
    • Anecdotal—severe maternal anxiety/stress and/or pain, such as severe laminitis
    • Moderate to severe endometritis and/or endometrial periglandular fibrosis
    • Lymphatic cysts—anecdotal
    • Chromosomal abnormalities
  • Xenobiotics
    • Ergopeptine alkaloids associated with fescue toxicosis or ergotism can be associated with placental thickening and abortion, although prolonged gestation is more common
    • Phytoestrogens—anecdotal abortions early in spring
    • Xenobiotics causing maternal disease, such as cardiac glycosides, taxine alkaloids, carbamates, organophosphates
    • Originally proposed with mare reproductive loss syndrome, but penetrating septic septal emboli now suspected
    • Equine protozoal encephalomyelitis therapies during pregnancy
  • Repeated large doses of corticosteroids during late gestationIatrogenic causes
    • Prostaglandin F2 alpha to terminate a pregnancy
    • Procedures mistakenly done on a pregnant mare, such as artificial insemination, intrauterine infusions, samples taken for cytology, culture, or biopsy
    • Possible mechanisms can involve the sequence of events below:
      • Fetal death/premature parturition—some intrinsic structural or functional defect or exposure to xenobiotics
      • Fetal expulsion <80 days of gestation after CL loss, a result of endometritis or other factors
      • Fetal death/expulsion by placental insufficiency or separation
      • Fetal stress, dead twin fetus, maternal stress, or combination
      • Fetal reabsorption, maceration, mummification, autolysis, death during delivery (stillbirth) or delivery of live fetus incapable of extrauterine survival

Systems Affected!!navigator!!

  • Reproductive
  • Other organ systems can be affected if there is maternal systemic disease

Signs!!navigator!!

Historical Findings

One or more of the following:

  • Signs consistent with labor at an unexpected stage of gestation
  • Dystocia, birth of nonviable foal
  • Previous history of abortion, dystocia, or birth of a nonviable foal
  • Vaginal discharge, which is generally mucoid, hemorrhagic, or serosanguineous
  • Premature udder development; dripping milk
  • Anorexia or colic
  • Recent systemic disease
  • Moderate/severe endometritis and/or endometrial periglandular fibrosis
  • None/excessive abdominal distention consistent with stage of gestation
  • Behavioral estrus in pregnant mare, which might be normal for stage of gestation and is dependent on time of year and stage of pregnancy when pregnancy is lost

Physical Examination Findings

  • Depends on the cause, time of fetal death, stage of gestation, duration of the condition, and whether pregnancy ended in dystocia or with RFM
  • Abortion usually occurs rapidly and is unobserved
  • Signs range from none to multisystemic and life-threatening disease
  • Most symptomatic spontaneous noninfectious abortions occur during the second half of gestation, characterized by one or more of the following physical examination findings:
    • Fetal/placental structures protruding through vulval lips; abdominal straining or discomfort
    • Premature placental separation (red bag)
    • Vulval discharge (variable appearance), premature udder development, dripping milk
    • Previously diagnosed pregnancy absent at next examination; fetal death determined by TRP or transrectal/transabdominal US
    • Twin fetuses
    • Placental separation or hydrops of fetal membranes
    • Signs of concurrent, systemic disease, dystocia, or RFM
  • Note that signs are extremely variable. Mares pregnant at early check can remain asymptomatic but abort. Abortion can be unobserved early in gestation, may be rapid without signs

Risk Factors!!navigator!!

  • Often nonspecific
  • See Pathophysiology

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Other Causes of Abortion

  • Infectious, spontaneous abortion
  • Placentitis

Other Causes of Signs of Labor or Abdominal Discomfort

  • Normal parturition
  • Dystocia unassociated with abortion
  • Prepartum uterine artery rupture
  • Colic associated with uterine torsion
  • Discomfort associated with hydrops of fetal membranes or prepubic tendon rupture
  • Colic unassociated with reproductive disease

Other Causes of Vulval Discharge

  • Normal parturition
  • Dystocia not associated with abortion
  • Normal estrus
  • Endometritis, metritis, or RFM, mucometra or pyometra

Diagnostic Procedures!!navigator!!

  • Asymptomatic unless—placentitis, secondary to endotoxemia, fetal expulsion associated with twins or dystocia
  • Definitive causative diagnosis of equine abortion occurs in ≈50–60% of all cases
  • Excluding twins and equine herpesvirus 1, the diagnostic rate may be only 30%
  • Note that unless the cause of the abortion is obvious, such as twins or iatrogenic, must rule out infectious causes, especially if multiple mares are affected or at risk:
    • CBC, serum biochemistry
    • Maternal P4 may be useful at <80 days of gestation
    • Maternal estrogen concentrations
    • Decreased maternal relaxin concentration associated with abnormal placental function
    • Decreased maternal prolactin secretion during late gestation—associated with fescue toxicosis and ergotism
    • Anecdotal reports of lower triiodothyronine/thyroxine levels with history of conception failure, early embryonic death, or abortion. The significance of low T4 levels is unknown and somewhat controversial
    • Test for PPID and EMS/IR
    • Cytogenetic studies—useful if maternal or fetal chromosomal abnormalities are suspected
    • Endometrial biopsy to assess endometrial inflammation and/or fibrosis
    • Vaginal speculum examination and hysteroscopy if structural cervical or uterine abnormalities are suspected
    • Xenobiotics—narrow testing to one or several potential xenobiotics in maternal and fetal samples. Might be very expensive, and unproductive. Feed or environmental analyses, for ergopeptine alkaloids, phytoestrogens, heavy metals, or fescue endophyte
    • Imaging with transrectal and transabdominal US can be used to evaluate fetal viability, placentitis, and alterations in appearance of amniotic and/or allantoic fluids, as well as other gestational abnormalities, such as hydrops
    • Collect samples for histopathology, cytology, microbiology, serology, and molecular testing procedures:
      • If available, fresh/chilled fetal thoracic or abdominal fluid and serum from the fetal heart or cord blood
      • Fetal stomach content
      • 10% formalin-fixed and chilled/frozen samples of fetal membranes fetal viscera

Pathologic Findings!!navigator!!

  • Macroscopic and histological evidence of physical causes (see Pathophysiology)
  • Twins—avillous chorionic membrane at point of contact between the fetal membranes
  • Umbilical cord torsion should be confirmed by evidence of vascular compromise
  • Villous atrophy or hypoplasia might suggest endometrial periglandular fibrosis and/or lymphatic cysts
  • Placental edema, gross and histopathological, is consistent with equine fescue toxicosis
  • Various placental abnormalities reported with foals resulting from SCNT cloning procedures

Treatment ⬆ ⬇

Outline

TREATMENT

Appropriate Health Care!!navigator!!

  • Except in cases of late-gestational placentitis (>270 days) and endotoxemia, no therapy indicated to preserve fetal viability with spontaneous, infectious abortion
  • For mares that abort, there is only prophylactic therapy for metritis or endometritis. Therapy is generally limited to intrauterine lavage, with or without antibacterial therapy
  • Preexisting GI disease and complications, such as laminitis, might warrant hospitalization and intensive care

Nursing Care!!navigator!!

Most affected horses require limited nursing care, except in instances of complications, e.g. septicemia, dystocia, RFM, metritis, and laminitis.

Activity!!navigator!!

There should be paddock exercise to permit observation; recommendation subject to change if the mare exhibits clinical signs of laminitis.

Diet!!navigator!!

Monitor feed and water intake, defecation, and urination; no particular dietary changes in the absence of GI disease or laminitis.

Client Education!!navigator!!

  • The increased survivability of twin foals has led some breeders and, even, veterinarians to be less concerned about twin pregnancies. However, the risk of abortion, dystocia, and neonatal complications associated with twins still warrants prevention and/or management and discussion of the inherent risks related to pregnancy ending in abortion or complicated delivery
  • Periglandular fibrosis is irreversible
  • Older mares or mares with preexisting systemic disease might be at increased risk of spontaneous abortion
  • Embryo transfer—especially mares with a history of abortion or those with severe endometrial periglandular fibrosis or severe structural abnormalities
  • Risks associated with ingestion of endophyte-infected fescue and/or ergotized grasses and grains
  • Inform owners of the possible complications of abortion

Surgical Considerations!!navigator!!

  • Dystocia or GI disease requiring surgical intervention
  • Reduction of twin pregnancies can involve surgical approaches for selected fetal decapitation or other means for elimination of one twin
  • Hysteroscopic removal of lymphatic cysts to prevent future abortions

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Altrenogest administered 0.044–0.088 mg/kg PO daily can be started later during gestation, continued longer, or used only for short periods of time, depending on serum P4 levels during first 80 days of gestation, clinical circumstances, risk factors, clinician preference. Note that serum levels reflect only endogenous P4, not exogenous, oral product
  • If near term, altrenogest frequently is discontinued 7–14 days before foaling date, unless indicated otherwise by fetal maturity/viability, or actual gestational age is in question

Precautions, Possible Interactions!!navigator!!

  • Altrenogest is only used to prevent abortion in cases of endotoxemia or placentitis (>270 days of gestation) if fetus is viable
  • Altrenogest is absorbed through skin; wear gloves and wash hands

Alternative Drugs!!navigator!!

  • Injectable P4 (150–500 mg oil base) IM
  • Newer, repository forms of P4 are occasionally introduced; however, some evidence of efficacy should be provided prior to use
  • Medications for preexisting maternal disease

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

  • At 7–10 days post abortion monitor uterine involution
  • Observe for any signs of systemic disease and laminitis
  • Assess genital tract health— ± vaginal speculum, hysteroscopy, uterine culture and cytology, endometrial biopsy
  • Base treatment on clinical results of these procedures
  • Uterine culture <14 days postpartum or post abortion is affected by contamination at the time of parturition (abortion)

Prevention/Avoidance!!navigator!!

  • Early recognition of at-risk mares
  • Record double ovulations
  • Early twin diagnosis (<25 days, as early as day 14 or 15)
  • Selective embryonic/fetal reduction involving transrectal, transvaginal, or transabdominal US or, potentially, surgery and induced death of one fetus
  • Manage preexisting endometritis before next breeding to minimize inflammation
  • Careful observation of pregnant mares, monitor mammary gland development
  • Remove mares from fescue pasture during last third of gestation (minimum 30 days)
  • Domperidone (1.1 mg/kg PO daily) at earliest signs of equine fescue toxicosis or 10–14 days prior to due date; continue until parturition and development of normal mammary gland
  • Injection with fluphenazine (25 mg IM in pony mares) on day 320 of gestation has been suggested for prophylaxis of fescue toxicosis
  • Careful use of medications in pregnant mares
  • Avoid exposure to known toxicants

Possible Complications!!navigator!!

  • Dystocia, other potentially life-threatening conditions
  • Future fertility and reproductive value can be impaired by dystocia, RFM, endometritis, laminitis, septicemia, trauma to genital tract
  • Potential complications associated with twin reduction increase the later in gestation they are attempted

Expected Course and Prognosis!!navigator!!

  • Most patients recover with appropriate treatment
  • Complications can involve significant impact on mare's survivability and future fertility
  • Guarded prognosis for pregnancy maintenance with severe endometritis and endometrial periglandular fibrosis

Miscellaneous ⬆ ⬇

Outline

MISCELLANEOUS

Synonyms!!navigator!!

  • Abortion
  • Spontaneous abortion
  • Noninfectious abortion
  • Twin abortion

Abbreviations!!navigator!!

  • CL = corpus luteum
  • EMS = equine metabolic syndrome
  • GI = gastrointestinal
  • IR = insulin dysregulation
  • P4 = progesterone
  • PPID = pituitary pars intermedia dysfunction
  • RFM = retained fetal membranes/placenta
  • SCNT = somatic cell nuclear transfer
  • TRP = transrectal palpation
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

Burns TA. Effects of common equine endocrine diseases on reproduction. VCNA Eq Pract 2016;32(3):435–449.

Gupta RC, Evans TJ, Nicholson SS. Ergot and fescue toxicosis. In: Gupta RC, ed. Veterinary Toxicology: Basic and Clinical Principles, 3e. New York: Academic Press, 2018:995.

McKinnon AO. Origin and outcome of twin pregnancies. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction, 2e. Ames, IA: Wiley Blackwell, 2011:2350–2358.

Pozor MA, Sheppard B, Hinrichs K, et al. Placental abnormalities in equine pregnancies generated by SCNT from one donor horse. Theriogenology2016;86(6):1573–1572.

Sebastian MM, Bernard WV, Riddle WT, et al. Review paper: mare reproductive loss syndrome. Vet Pathol 2008;45:710–722.

Troedsson MHT, Macpherson ML. Placentitis. In: McKinnon AO, Squires EL, Vaala WE, Varner DD, eds. Equine Reproduction, 2e. Ames, IA: Wiley Blackwell, 2011:2359–2367.

Author(s) ⬆

Author: Tim J. Evans

Consulting Editor: Carla L. Carleton