Investigating the pathogenesis of high-serum gamma-glutamyl transferase activity in Thoroughbred racehorses: A series of case-control studies.
Authors: Mann Sabine, Ramsay Joshua D, Wakshlag Joseph J, Stokol Tracy, Reed Steven, Divers Thomas J
Journal: Equine veterinary journal
Summary
# Editorial Summary: High-Serum GGT Activity in Thoroughbred Racehorses Elevated serum gamma-glutamyl transferase (GGT) has long been suspected as a marker of training maladaptation and poor racing performance in Thoroughbreds, yet its underlying cause remained unclear until this investigation. Mann and colleagues conducted paired case-control studies across multiple racing stables (54 horses total, with cases defined as GGT ≥50 IU/L versus controls at 19–28 IU/L) and performed comprehensive serum biochemistry, viral screening, metabolomic analysis, and micronutrient profiling to identify potential infectious or metabolic drivers. Viral hepatitis—specifically equine hepacivirus and parvovirus-hepatitis—was ruled out as a contributing factor, but elevated cases showed mild hepatocellular and cholestatic markers alongside distinct metabolic fingerprints: increased pyroglutamic acid and taurine-conjugated bile acids, reduced vitamin B6, and lower selenium concentrations despite most values remaining within reference ranges. These findings suggest high GGT syndrome represents a complex metabolic disorder characterised by oxidative stress and impaired bile acid metabolism, rather than a simple infectious process. For practitioners, this underscores the importance of investigating suboptimal training response through metabolic lenses—evaluating antioxidant status, liver function patterns, and selenium adequacy—rather than assuming viral infection, whilst recognising that GGT elevation likely reflects multiple concurrent physiological stressors rather than a single pathological cause.
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Practical Takeaways
- •High GGT in racehorses is not caused by viral hepatitis; veterinarians should investigate metabolic dysfunction and oxidative stress as primary mechanisms
- •Monitor selenium status and B vitamin supplementation in horses with elevated GGT, even when laboratory values appear normal
- •Consider high GGT a marker of metabolic imbalance affecting training adaptation rather than infectious disease, requiring nutritional and metabolic assessment
Key Findings
- •High GGT syndrome is a complex metabolic disorder unrelated to equine hepacivirus or parvovirus-hepatitis in this cohort
- •Case horses showed increased pyroglutamic acid and taurine-conjugated bile acids with reduced Vitamin B6 compared to controls
- •Selenium concentrations were lower in high-GGT cases despite being within or above reference intervals in both studies
- •Mild increases in hepatocellular injury and cholestatic markers in cases suggest oxidative stress and cholestasis contribute to pathophysiology