Laboratory Testing Can Help Pinpoint Cause of Abortion

When a mare aborts a foal, it can be a traumatic event for both horse and owner. While emotionally and financially expensive, abortion is not terribly uncommon in the equine breeding business. As many as 30% of broodmares fail to produce a live foal.

Equine abortion describes the loss of a fetus before it is viable--between 50 to 300 days of pregnancy. Before then, it is considered an early pregnancy loss, with the embryo reabsorbed in the mare’s body. After 300 days, the foal is considered stillborn because many foals born alive at that point are able to survive.

When an abortion occurs, it is important to find the cause. Some conditions that lead to abortion occur sporadically and involve a single mare. Other conditions might be infectious or contagious, which can cause an outbreak of abortions in mares in a particular area.

Common causes of abortion related to an individual mare include conformation problems involving the vulva, cervix, or vaginal canal. Conformation problems can allow bacteria to enter the uterus, causing infections like placentitis (inflammation of the placenta). Other problems include abnormalities with the placenta or umbilical cord, and twinning.

While twin foals may be an exciting prospect, caution is warranted because twinning is the most common non-infectious cause of abortion in mares, and usually occurs early on or after the sixth month of pregnancy.

Infectious causes of abortions include viral infections like equine herpesvirus (EHV) and viral arteritis (EVA), as well as fungal or bacterial infections such as Streptococcus equi, E. coli, and leptospirosis. In addition to twining and umbilical cord defects, congenital defects of the foal and some trace mineral deficiencies are other potential causes. Abortion might also occur after severe illness, colic, or surgery.

Signs that a mare is about to abort include mammary gland development and lactation or "bagging up," stretching of the vulva, increased vaginal discharge, overt abdominal edema, or if the mare displays symptoms of mild colic. If these signs occur in mid to late pregnancy, a veterinarian should be contacted immediately.

If an abortion does occur, samples of the fetus, placenta, and blood from the mare can be sent to a diagnostic lab such as the Washington Animal Disease Diagnostic Laboratory (WADDL) in Pullman for a diagnosis.

"The tissue samples must be obtained fresh from the placenta and fetus within the first 24 hours after an abortion occurs from the mare, but the earlier the better," said Ahmed Tibary, DVM, PhD, Dipl. ACT, associate professor at WSU. "There are some conditions we can prevent, and some that we can’t, but the cause should be determined.

"To get a precise diagnosis, samples must be submitted to WADDL correctly and in good condition," he said. "The WADDL Web site ( includes a form that describes what tissues should be collected and how to submit them. A veterinarian should always be contacted to help with this, and to check the mare to make sure she expelled the entire placenta and that she is recovering."

With a diagnosis, owners are in a position to make decisions about whether to breed their mare again and to prevent other abortions from happening to other mares in their herd or the local region.

"Viral causes can be managed with proper biosecurity measures and vaccinations. Vaccination is important because infected mares can easily infect other mares," Tibary said.

Biosecurity measures help prevent outbreaks by isolating mares with an infectious disease and practicing good sanitation while caring for sick mares. Other non-infectious conditions that lead to abortion might also be correctable through medical means or through frequent pregnancy evaluations for mares that are deemed high risk.

"Those with bacterial infections that cause placentitis can be managed medically if the infection is detected early," Tibary said. "There are also surgical procedures to help prevent ascendant infections in mares with vulvar/vaginal conformation problems."

For more information about submitting samples to the Washington Animal Disease Diagnostic Laboratory, contact the Laboratory at 509/335-9696 or  

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