Agents of Abortion: Why Pregnant Mares Abort

The first step toward preventing pregnancy loss in horses is understanding why it happens in the first place.

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Agents of Abortion
Understanding the cause of abortion can help breeders and veterinarians manage the mare going forward for future successful pregnancies. | Photo: iStock

The first step toward preventing pregnancy loss is understanding why it happens in the first place

As horse breeders eagerly await the impending birth of their foals, they can’t help but fear one thing: abortion. Abortion is foal loss before 300 days of gestation. In worst-case scenarios, breeding facilities don’t lose just one foal; a pathogen causes an abortion storm in which several mares lose their pregnancies around the same time. Regardless of the magnitude of losses, abortion can be a devastating emotional and financial blow to a horse owner.

It’s important to understand the various reasons mares abort and know whether yours is at risk. Keep in mind, however, that abortion causes differ based on geographic location. In this article we’ll review some of the most common infectious and noninfectious causes.

Infectious Causes

Equine herpesvirus-1 (EHV-1)

Peter Timoney, MVB, PhD, FRCVS, is the Frederick Van Lennep Chair in Equine Veterinary Science at the University of Kentucky and a designated world expert on equine rhinopneumonitis and equine viral arteritis for the World Organization for Animal Health. He says the most important cause of abortion in mares in the United States is equine herpesvirus-1, also known as equine rhinopneumonitis

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Written by:

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

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