MSD Manual

Please confirm that you are a health care professional

honeypot link
Professional Version

Abortion in Horses

By

Patricia L. Sertich

, MS, VMD, DACT, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania

Last full review/revision Feb 2021 | Content last modified Mar 2021
Topic Resources

Twin pregnancy is the most common noninfectious cause of abortion in mares Abortion in Horses Twin pregnancy is the most common noninfectious cause of abortion in mares. In most cases, uterine capacity and subsequent placentation are inadequate to support two fetuses to term. Although... read more Abortion in Horses . In most cases, uterine capacity and subsequent placentation are inadequate to support two fetuses to term. Although twins may spontaneously reduce to a viable singleton early in gestation (<60 days),="" visible="" abortions="" tend="" to="" be="" seen="" after="" 7–9="" months.="" premonitory="" clinical="" signs="" of="" impending="" abortion="" may="" be="" only="" premature="" mammary="" gland="" development.="" fetal="" membranes="" should="" always="" be="" examined="" for="" large="" avillous="" areas="" on="" the="" chorion,="" located="" where="" the="" twin="" conceptuses="">

Because of the risk of abortion and dystocia Dystocia in Horses Most causes of dystocia in the mare are due to abnormal presentation, position, or posture. A dead or compromised fetus often is not properly positioned in the pelvic canal. Dystocia due to... read more Dystocia in Horses in a mare carrying twins, if twins are detected by ultrasonography per rectum at <30 days,="" reduction="" to="" one="" embryo="" by="" manual="" crushing="" per="" rectum="" is="" recommended.="" between="" 30–60="" days="" of="" gestation,="" transvaginal="" aspiration="" of="" one="" conceptus="" may="" result="" in="" a="" viable="" singleton.="" at="" approximately="" 60="" days="" of="" gestation,="" one="" fetus="" may="" be="" eliminated="" by="" cervical="" dislocation.="" after="" 110="" days="" of="" gestation,="" one="" twin="" may="" be="" reduced="" by="" intracardiac="" injection="" of="" potassium="" chloride="" or="" procaine="" penicillin,="" guided="" by="" transabdominal="" ultrasonography.="" success="" rates="" vary="" depending="" on="" the="" procedure="" performed,="" the="" experience="" of="" the="" veterinarian,="" and="" the="" character="" of="" the="" pregnancy.="" pregnancy="" should="" be="" sonographically="" monitored="" periodically="" after="" twin="">

Abortion in Horses

The most common cause of viral abortion in mares is equine rhinopneumonitis, which is caused by equine herpesvirus 1 (EHV-1). These abortions occur predominantly in the last trimester and usually are not associated with a respiratory infection. All pregnant mares should be vaccinated against EHV-1 at 5, 7, and 9 months of gestation.

The equine arteritis virus can cause equine viral arteritis (EVA) abortion. An EVA-seronegative mare scheduled to be bred to an EVA-positive stallion that is shedding the arteritis virus in the semen should be vaccinated before breeding. Horses must be isolated for 3 weeks after EVA vaccination. Mares should not be vaccinated against EVA during pregnancy. EVA-negative mares bred to EVA-positive, viral-shedding stallions will become infected, shed virus, and seroconvert.

Sporadic abortions due to placentitis can be caused by bacterial and mycotic infections of the placenta. These are predominantly ascending infections acquired through the caudal genital tract but may also be focal or diffuse. Bacteria involved often include Streptococcus zooepidemicus, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, Rhodococcus equi, or Actinobacillus equuli. Mycotic organisms include Mucor and Aspergillus spp. Efforts to reduce the incidence of these abortions should include good breeding hygiene, treatment of genital disease before breeding, maintaining good body condition throughout pregnancy, and vulvoplasty (Caslick operation) to prevent pneumovagina. Mares at risk of placentitis should be examined by ultrasonography per rectum periodically during late gestation for evidence of genital infection and placental abnormalities as evidenced by uterine discharge and increased uteroplacental thickness.

Any aborted fetus and fetal membranes should promptly be submitted fresh or cooled (never frozen) to a diagnostic laboratory to determine the cause of the abortion.

For More Information

quiz link

Test your knowledge

Take a Quiz!
iOS ANDROID
iOS ANDROID
iOS ANDROID
TOP