Link Between Liver Virus and Poor Performance in Horses Questioned

Researchers at Cornell University believe equine parvovirus-hepatitis virus (EqPV-H) causes poor performance in athletic horses, including racehorses.^*

“Poor performance describes horses that simply are not living up to athletic expectations. Many health conditions can contribute to poor performance, including inflammatory airway disease, dynamic upper airway conditions such as dorsal displacement of the soft palate, or even tying-up,” explained Kathleen Crandell, Ph.D., a nutritionist for Kentucky Equine Research. Add EqPV-H to that list of possibilities.

Since researchers first identified the virus in 2018, genetic material (DNA) of EqPV-H virus has been found in between 7% and 37% of tested horses around the world. Experimental studies found that the virus has an affinity for the liver, resulting in subclinical or mild disease, meaning these horses show little to no sign of liver infection. However, infection may result in elevations in liver enzymes, such as gamma-glutamyl transferase (GGT), aspartate aminotransferase, and alkaline phosphatase.

Interestingly, about 37% of racehorses diagnosed with GGT syndrome tested positive for EqPV-H.

Despite being commonly found in horses, the relevance of EqPV-H in horses remains unclear. Should horse owners and trainers be concerned about horses that test positive for EqPV-H?

To gain additional information on this virus, Cornell researchers collected 191 liver samples from Thoroughbred racehorses from New York state. Total DNA was extracted from the liver samples and tested for the presence of EqPV-H DNA. Sections of liver samples that tested positive for EqPV-H DNA were examined microscopically to directly visualize the location of that viral DNA.

Of the 119 liver samples, 42 (22%) were positive for EqPV-H, which was similar to previously reported rates of infection. Viral DNA was subsequently found in 31 of those 42 liver samples evaluated microscopically, with the DNA found in necrotic (dead) areas of liver tissue in 11 of the 42 samples (26%).

“This means that naturally acquired EqPV-H infection appears to cause mild hepatitis with liver cell necrosis. The overall impact of this mild hepatitis on racehorse performance, however, needs further evaluation,” Crandell said.

As mentioned above, many causes of poor performance exist, potentially including poorly described conditions such as liver disease, EqPV-H, and GGT syndrome.

“Oxidative stress could play a role in poor performance, including GGT syndrome. Nutritional strategies can manage oxidative stress, such as supplementing the horse’s diet with an antioxidant such as Nano-Q10, which contains a highly available source of coenzyme Q10,” she recommended.

^*Jager, M.C., J.E. Tomlinson, C.E. Henry, M.J. Fahey, and G.R. Van de Walle. 2022. Prevalence and pathology of equine parvovirus-hepatitis in racehorses from New York racetracks. Virology Journal 19(1):175.