A Threat for Breeding Operations

While equine herpesvirus (EHV) is typically associated with respiratory illness in young equine athletes, it can also have devastating consequences for breeding operations. As foaling season approaches, it’s important for horse owners to understand the risks EHV poses to broodmares. Dr. Tracey Chenier, an associate professor of theriogenology at the Ontario Veterinary College, provides insights on the prevalence of the virus and strategies breeders can use to protect their mares.

According to Dr. Chenier, research indicates that 50 to 80 percent or more of horses carry antibodies to EHV, meaning they’ve been exposed to the virus at some point, even if they didn’t show symptoms. While many people associate EHV with respiratory illness, which can easily spread through showgrounds or racing barns, the virus can also lead to abortions in pregnant mares. Initially, EHV infects the respiratory system but can then move to the lymphatic system, spreading throughout the body and posing a serious risk to a pregnancy.

The virus is often discussed in the context of respiratory illness spread through nasal secretions. However, Dr. Chenier emphasizes that if EHV causes an abortion, the tissues and fluids from the mare and aborted fetus are “absolutely full of the virus,” and must be treated as biohazards, especially if there are other pregnant mares on the farm.

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Because many horses infected with EHV don’t show symptoms while shedding the virus, it’s impossible to know for sure if a mare is a carrier, posing a threat to others. Silent carriers of the virus may shed it intermittently, triggered by various stressors including physical, environmental, mental, or social factors.

“Remember that in the case of herpesvirus, the infection’s taking place weeks or even months before the abortion,” Dr. Chenier explains. “The abortion’s just the later result of that infection. Other than good biosecurity following an abortion to reduce the risk for other mares on the farm, there’s not really a treatment, per se.”

Related: Equine Infection Control: Strategies to Prevent Transmission

Dr. Chenier also notes that vaccinating for EHV during an outbreak is a controversial topic. However, in some cases, it may be advisable depending on the mare’s most recent vaccination history.

As foaling season approaches, the Ontario Animal Health Network has released a podcast for horse owners about the dangers of Equine Herpesvirus for broodmares.

Listen: Equine Reproduction Expert Tells You What You Need To Know About Equine Herpesvirus - Paulick Report | Latest news and commentary from the horse racing and equine world

Information provided by Paulick Report.

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Photo: Shutterstock/Shawn Hamilton