Quick & Clean Guide To Equine Abortion

Quick & Clean Guide To Equine Abortion 19 September, 2011
– Dr Sarah Seitz

There are many reasons for equine abortion. The more common causes that I will discuss include placentitis, viral abortion, and non-infectious causes of abortion such as twin foetuses and umbilical torsion.

Some Key Points:

– Placentitis(inflammation of the placenta) is a common cause of abortion and is commonly caused by bacteria including Streptococcal species and E. coli. Treatment includes the use of antibiotics, anti-inflammatory drugs and medications to maintain uterine quiescence.

– The most commonly implicated viral cause of abortion is equine herpesvirus type 1 (EHV-1) which typically causes abortion in the last trimester. An effective vaccine is available for EHV-1 and should be given at 5, 7, and 9 months of gestation.

– The most common cause of non-infectious abortion is twin foetuses; the mare’s placenta generally cannot maintain two foetuses; however, occasionally, twin foetuses will be born alive.


Placentitis is a major cause of abortion in mares during the later stages of pregnancy. The most common route in which bacteria enter into the utero-placental unit is via ascending infections (through the vagina), which causes inflammation and placental detachment at the cervical star. Hematogenous infection (bacteria enter the placenta via the blood) is also possible. Bacteria such as Streptococcus zooepidemicus, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella are some of the more common bacterial isolates from mares with placentitis. The placenta becomes inflamed and thickens which causes it to separate from the endometrium, which ultimately leads to abortion. The inflammation may also promote uterine activity. Treatment options for mares with placentitis include the following:

– Antibiotic therapy (particular antibiotic depends of the type of bacteria responsible)
– Non-steroidal anti-inflammatory drugs (Flunixin meglumine) to reduce inflammation

The outcome of placentitis can be variable ranging from abortion to birth of a healthy foal to birth of a septic foal. Early detection and treatment is important. If you suspect placentitis, ask your veterinarian to do an ultrasound to measure the combined utero-placental thickness (CUPT). Early treatment results in the best outcome.

Viral Abortion:

Viral infections in horses are another prevalent cause of abortion. The most common virus incriminated is equine herpesvirus type 1 (EHV-1), but EHV-4 and equine viral arteritis (EVA) may also cause abortion. Currently, the use of vaccination programs against EHV-1, given at 5, 7, and 9 months of pregnancy, has reduced the incidence of EHV-1 induced abortions. Abortion may occur soon after the mare is infected or may occur several weeks thereafter. When the foetus is infected during a viremic episode (virus present in the blood), the placenta can detach from the endometrium resulting in abortion. The foetus can become infected by the blood vessels in the chorion, or by inhalation of infected amniotic fluid. If you suspect your mare has aborted due to herpes virus, it is important to collect the whole foetus if possible, as well as the placenta, and submit it for necropsy. Some foetuses may be born alive and have neonatal herpes virus infection. Many of these EHV infected foals do not survive for longer than a few hours or days, and generally show signs of respiratory distress, icterus (jaundice), fever, and lethargy. There is no direct treatment of EHV infection in the mare or infected neonatal foal, although antiviral medications such as acyclovir and valacyclovir may theoretically be beneficial, although this is expensive.

Prevention by the use of stringent vaccination protocols against EHV is by far the best strategy to avoid losses by EHV.

Twin Foetuses:

Mares have a diffuse microcotyledonary placentation which makes it unlikely for a twin pregnancy to be carried to full-term because of the limited endometrial surface that is available for the allantochorion to attach. The two foetuses will compete for adequate nutrition and placentation. If the twin pregnancy is maintained to the later stages of pregnancy, foetal growth becomes more rapid and demanding on the mare until one, or both, foetuses become progressively emaciated and abort. If twin foetuses are carried to full term, often one, or both, of the foetuses are stunted in growth and size from intrauterine growth retardation. Although it is possible for both twins to survive, both foals are usually smaller and weaker than usual, and generally have some form of developmental disorder.

Umbilical Torsion:

Umbilical torsion is a relatively uncommon cause of abortion in the mare. The foetus is able to rotate in the amniotic sac and can result in excessive twisting of the umbilical cord. This causes constriction of the normal flow of blood through the umbilical cord along culminating in foetal death.

Although there are many more causes of abortion in horses, this article summarizes the most common causes generally seen on stud farm.

Good luck with the rest of the foaling season and I hope your foals are delivered alive and healthy!

Sarah Seitz was born in Zimbabwe and moved to South Africa when she was 10 years old. After attending high school at St Andrew’s in Johannesburg, she worked for her father for several years doing wildlife conservation and breeding endangered species. After that, she was introduced to the illustrious world of thoroughbred breeding and racing when she was employed to manage a thoroughbred stud farm for four years. This stud has produced several notable winners in its time, including a Durban July winner.

She found herself really enjoying the veterinary aspect of equine management and breeding, so decided to come the USA to study Veterinary Medicine. Far from home and lots of paperwork later, she completed her undergraduate BSc degree at the University of Kentucky in Lexington, and she is currently in her final year of Veterinary Medicine at Washington State University in Pullman, Washington. Sarah’s primary veterinary interest is large animal medicine and theriogenology. Sarah also enjoys volunteer work and has traveled to several countries including India, Nicaragua and Ecuador to provide free veterinary services to underdeveloped communities.

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