The Kester News Hour at the annual American Association of Equine Practitioners Convention highlight key advancements in equine research worldwide. In 2024’s edition Carrie Finno, DVM, PhD, Dipl. ACVIM, professor of veterinary genetics and the Gregory L. Ferraro Endowed Director of the Center for Equine Health at the University of California, Davis, and Katie Seabaugh, DVM, Dipl. ACVS, ACVSMR, associate professor of equine sports medicine and rehabilitation at Colorado State University, in Fort Collins, shared their top picks from recent studies in their areas of practice interest.

Studying Graying Speed and Melanoma in Horses

Finno began with research by Rubin et al. (2024), in which researchers identified a genetic variation in horses that determines their greying speed and melanoma incidence.

“Graying is caused by a duplication of a 4.6 kb (kilobase, a unit of measurement used to help designate the length of DNA or RNA) intronic sequence in syntaxin 17 (STX17),” said Finno. “If horses have one copy of the variant, then they are not gray. Gray horses with two copies of STX17 gray slowly and have lower rates of melanoma but, if a horse has three copies, then they are the fast-graying horses linked with melanoma.”

For example, if a gray mare has the genes G3/G1 and the gray stallion is G3/G1, then the foal could be G3/G3, meaning he or she will gray very fast and has a higher likelihood of developing melanoma. The results could lead not only to better identification of horses likely to gray early or pass on gray-with-age genes but also to a better understanding of how the mutation affects horses’ health.

Detecting Atrial Fibrillation in Horses

In the second study Finno covered (Vernemmen et al., 2024), researchers described a method for veterinarians to detect atrial fibrillation in horses using an implantable loop recorder (ILR).

The ILRs can be placed under the skin in the left lateral thorax overlying the heart, said Finno. Practitioners use these to detect arrhythmias as a possible cause of collapse, poor performance, or monitor for atrial fibrillation (AF) recurrence in a research setting. The device can now collect information and email the clinician, improving the speed with which AF can be identified.

“Be aware that some false positives can be a result of bradycardia (when the heart beats slower than normal) rather than AF because it is a human product,” said Finno. “And we need to appreciate that AF is likely genetic.”

Identifying A Cause of Neck Pain in Horses

Seabaugh presented a study (Hendersen et al., 2024) in which researchers described the incidence of neck pain without neurologic disease in horses with transposition of the ventral lamina from C6 to C7 of the cervical vertebrae.  

“The ventral lamina is part of the transverse process, and this ventral aspect of C6 can move to the C7 vertebra,” said Seabaugh. “When located on C6, the longus colli muscle attaches to the ventral lamina, which is a cervical flexor. Movement of the transverse process likely affects the biomechanics of the neck.”

In the retrospective study, researchers looked at radiographs taken from 2020 to 2022, including a total of 135 horses. Reasons for radiographs included routine neurologic exam, neck pain, and performance-related behavior changes.

Key findings were:

1. The researchers saw transposition in 20% of the horses that was not significantly associated with a final diagnosis, meaning an equal number of horses with or without the transposition fell into each diagnosis; and
2. Transposition was more common in horses that demonstrated pain during palpation of the neck (31%) than those without pain (18%).

Additionally, 63% (17 out of 27) of the horses with transposition were Warmbloods.

Prevalence of Neck Pathology in Warmblood Horses

Looking at Warmbloods more closely, Seabaugh presented a second study (Sue Dyson et al., 2024) where researchers described the prevalence of C6 and C7 transposition in the breed.

“This study included only Warmbloods: 127 controls and 96 horses with neurologic abnormalities, neck pain or stiffness, or neck-related forelimb lameness,” Seabaugh said. The researchers found 24.2% of horses had C6 and C7 transposition. Horses without neurologic issues (the controls) were more likely to have this variation than those with neurologic abnormalities.

“The conclusion from both studies was that there is no association between C6/7 transposition and neurologic disease, and it is just a variant occurring in up to one-quarter of all horses,” said Seabaugh.

Updated ACVIM EHV Consensus Statement

Finno broke down the updated ACVIM consensus statement for equine herpesvirus (Lunn et al., 2024) for the audience.

Three key takeaways from the new guidelines included:

1. Researchers have seen minimal evidence that the vaccine protects horses against equine herpesvirus-1 infection, but they still recommend vaccinating.
2. Pharmacological treatments have minimal effect (except valacyclovir if administered in advance).
3. In large outbreaks nasal swabbing typically suffices for diagnosing affected horses; however, when abortion occurs on the premises, veterinarians need to test blood samples.

In a study following the herpesvirus outbreak in Valencia, Spain, “Sixty-eight percent of horses with neurologic disease returned to exercise, and over half returned to full performance,” said Finno. “But the less ataxic they were on presentation, the more likely they were to fully recover. If there was urinary and vascular compromise, then they were more likely to be euthanized.”