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Equine Abortion

A Timetable Guide to Diagnosis by Lauri Robinson, Diagnostic Pathology Clerk edited by Wm. Van AIstine,DVM,PhD

Cause of Abortion/ Time of Gestation Gross Findings and Clinical Signs Diagnosis: Samples to Submit and Lab
Procedures (see note)
Early Embryonic Death (EED)
0-40 d Eariy Fetal Death


Maternal malnutrition, twin pregnancy, history of maternal stress, uterine disease, poor conformation of vulva, vagina, cervix

Early (EED) signs: often none

Later (EFD) signs: aborted fetus
Repeated gynecologic exams, fetal and maternal serum samples, antigen/ antibody compatibility
Equine Viral Arteritis
(EVA) 5-10 mo


Mare: depression, fever, anorexia,leukopeniakeratitis, diarrhea, colic, edema of limbs and ventral abdomen, generalized vascular necrosis Fetus: aborted 7-10 d after first signs of illness in mare, usually autolyzed because death 2-4 d prior to abortion, ± pleural effusion, petechial hemorrhage, if non-autolyzed- usually no gross lesions Histopath
-Virus isolation
-Check stallion since virus can be transmitted via semen
Twinning 6-9 mo (=most common non-infectious cause) Fetus: 2 feti, one in all of 1 horn and most of body. and the other in a small portion of the body and in the other horn
Placenta: large smooth area between the chorions of the twins
Mare: ± history of double ovulations
None needed
Placental Defects
Pathologic Twisting of the Cord
6-9 mo
Fetal anoxia due to pathologic twisting of the cord diagnosed by twisting of the cord and localized swelling and discoloration of the cord, causing vascular obstruction. Cord is usually abnormally long (>90 cm). Histopath Optional
Body Pregnancy
7-9 mo


Fetus: in the body of the uterus with stunted growth
Placenta:Placential insufficiency: homs have failed to expand and the chorioallantoic homs are undeveloped
None Necessary
9-1 Imocan be 5-11 mo
(#1 cause of abortion)


Fetus: Aborted 3 wks - 4 mo post mare exposure
-Liver: enlarged with subcapsular pinpoint to 5mm grey/ white foci of necrosis

-Lungs: severe edema,esp.interlobular septa, ± white foci of necrosis (like liver)

-Pleural/Abdominal cavities: excessive yellow fluid

± Pericardial effusion and epicardialpetchiae

± jaundice of mucous membrane

If bom alive - dies within hours to days

Placenta:±edematous, ± no rupture of cervical star,fetus usually still attached to fetal membranes,

± premature placental separation

Mares/Farm; asymptomatic/abortion storms
-Tissues in formalin for histopath-intra­nuclear inclusion bodies
-Virus isolation (fetal lung, liver, adrenal, lymph nodes)
-Fetal serology


Cause of Abortion/ Time of Gestation Gross Findings and Clinical Signs

Diagnosis: Samples to Submit and Lab Procedures (see note)
MycoticS-11mo (can be 5-11 mo) Most common:
(canbeA/ycor,Allescheria, Candida,Coccidiodes,Histoplasma,
Fetus: not autolytic, small, emaciated, if bom alive-dies soon after birth, ± bronchopneumonia±grey nodules on lung, ±mycotic dermatitis
Placenta: thickened, necrotic placenta ± necrotic plaques on maternal chorionic surface and on endometrium.
Note: it is normal for the equine placenta to have 1-2 mm hyperkeratotic nodules on the fetal side of the allantoamnionnear the major vessels of the cord.
Mares: post-abortion: purulent vulval discharge that resolves spontaneously
-fungal culture of placenta


Premature Placental Separation
late in gestation
Fetus: death by anoxia
Mares:allantochorion bulges out of vulvawith cervical star intact. Cause unknown
None necessary
Bacterial anytime most common:
others: E.coli, Pseudomonas,Staph., Klebsiella,Enterobacter, Taylorellaequigenitalis(CEM)
Usually ascending infection

Fetus: gross lesions are non-specific, ± enlarged liver, ± increased fluid in body cavities; organisms most consistently isolated from fetal stomach contents

Placenta: area of the chorioallantois around the cervical star is edematous and thickened, ± chorion covered in brown exudate, line of demarcation between the diseased placenta and normal chorioallantois, ± cloudy fluid in amniotic cavity
Length of pregnancy before abortion depends on the presence of absence of septicemia and the amount of placental involvement


-Fetal stomach contents, placenta, liver, kidney, and lung for culture
Leptospirosis 6-11 mo Fetus:icterus, enlarged/yellow liver
Placenta: thickened allantochorion or exudate
-Immunofluorescencefor spirochetes in aborted tissues (kidney, liver, placenta)


Other Causes of Equine Abortion:

Hormones: Progesterone deficiency, prostaglandin F2a, oxytocin,glucocorticoidsPoisonous Plants, Drugs: Fescue, locoweed, sudan grass, sorghum, phenothiazine,organophosphates thiabendazole

Notes: The best method of diagnosing equine abortions is to submit the entire fetus and placenta to a diagnostic laboratory. However, this is not always practical. If a field necropsy is performed, it is important that the practitioner send the following tissues to the diagnostic laboratory: placenta, lung, liver, spleen kidney, stomach contents, lymph nodes, thymus, fetal adrenal, and fetal serum.


Kobluk,C,etal. The Horse: Diseases and Clinical Management. Philadelphia: WBSaunders, 1995. McKinnon,AO and JLVoss.Equine Reproduction. Philadelphia: Lea & Febiger, 1993.


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