The prevalence of elevated gamma-glutamyltransferase and sorbitol dehydrogenase activity in racing Thoroughbreds and their associations with viral infection.
Authors: Ramsay J D, Evanoff R, Mealey R H, Simpson E L
Journal: Equine veterinary journal
Summary
# Editorial Summary Elevated gamma-glutamyltransferase (GGT) activity in racing Thoroughbreds correlates with training intensity and performance deficits, yet the underlying causes remain poorly characterised in North American populations. Ramsay and colleagues investigated whether four emerging hepatotropic viruses—equine pegivirus, hepacivirus A, pegivirus D (Theiler's disease virus), and equine parvovirus-hepatitis—might explain the prevalence of elevated liver enzyme activity in racehorses, hypothesising these subclinical viral infections drive hepatic inflammation without necessarily causing overt clinical disease. The researchers determined the frequency of elevated GGT (≥100 IU/L) and sorbitol dehydrogenase activity in their Thoroughbred cohort and examined associations between these markers and viral infection status using serological and molecular diagnostic methods. Detection of these viruses in animals with elevated liver enzymes suggests that subclinical viral hepatopathy may be more prevalent than previously recognised, potentially explaining performance issues in trained racehorses that lack obvious clinical signs. For practitioners managing racing stock, these findings underscore the importance of investigating viral status in horses presenting with persistently elevated liver enzymes, particularly when training duration or intensity appears insufficient to account for the biochemical abnormalities, and highlight a possible avenue for targeted management or monitoring protocols in affected individuals.
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Practical Takeaways
- •Monitor liver enzyme activity (GGT and SDH) in racehorses as elevated levels correlate with training load and poor performance outcomes
- •Consider screening racing Thoroughbreds for emerging hepatotropic viruses as potential contributors to unexplained elevated liver enzymes
- •Elevated liver enzymes in racehorses warrant investigation for viral infection, not just attributing changes to training intensity alone
Key Findings
- •Serum GGT activity in racehorses is positively correlated with cumulative days in training
- •GGT activity ≥100 IU/L has been associated with poor racing performance
- •Four emerging viruses (PgV E, HcV A, PgV D, EqPV-H) have been identified in horses with clinical and subclinical hepatopathy
- •These viruses may commonly infect racehorses and contribute to increased liver enzyme activity in the racing population