A new research study published in the Equine Veterinary Journal was titled, "Investigating the pathogenesis of high‐serum gamma‐glutamyl transferase activity in Thoroughbred racehorses: A series of case‐control studies." The research was authored by Sabine Mann, Joshua D. Ramsay, Joseph J. Wakshlag, Tracy Stokol, Steven Reed and Thomas J. Divers.
High‐serum γ‐glutamyl transferase (GGT) activity has been associated with and thought to be a marker of maladaptation to training and possibly poor performance in racehorses, but the cause is unknown. This study aimed to evaluate the role of oxidative stress, cholestasis, liver injury and infection with equine hepacivirus (EqHV) or equine parvovirus-hepatitis (EqPV-H) infection in racehorses with increased serum GGT activity.
The work started with a pilot study with eight horses with elevated serum GGT activity (≥50 U/L) and eight controls with normal GGT activity. This was followed by a larger study with 27 case-control pairs from three different yards. Serum liver chemistries, selenium measurements, viral PCR and metabolomics were performed.
With both studies combined, the overall prevalence of EqHV was 9% and the overall prevalence of EqPV-H was 36%. There was no difference in prevalence or copy numbers between cases and controls for either virus. Cases had decreased serum selenium concentrations, higher serum glutamate dehydrogenase (GLDH) and alkaline phosphatase (ALP) activities, and higher serum bile acid concentrations compared to controls.
Metabolomics findings were not consistent between the two studies, with different metabolites emerging from each analysis.
The authors concluded that the mechanism underlying high GGT activity in this population is likely complex and multifactorial, involving hepatic injury and possible cholestasis as well as oxidative stress.
Bottom line: EqHV or EqPV-H infections are unlikely to be the primary cause for the high GGT syndrome seen in Thoroughbred racehorses.
You can find a link to the article here from the Wiley Online Library of the British Equine Veterinary Association.