Elevations in serum muscle enzyme activities in racehorses due to unaccustomed exercise and training.
Authors: Mack S J, Kirkby K, Malalana F, McGowan C M
Journal: The Veterinary record
Summary
# Editorial Summary: Serum Muscle Enzymes and Training-Induced Muscle Stress in Racehorses Whilst hereditary muscle disease in racehorses is well documented, understanding how unaccustomed and cumulative training affects muscle breakdown remains poorly characterised. Mack and colleagues compared serum muscle enzyme activities (aspartate aminotransferase, creatine kinase and gamma-glutamyl transferase) across three groups: sedentary horses, two-year-old racehorses beginning training for the first time, and experienced three-year-old racehorses during their competitive season. Two-year-olds showed significant month-on-month elevations in aspartate aminotransferase over their first four months of training, whilst experienced horses demonstrated progressive increases in both aspartate aminotransferase and gamma-glutamyl transferase that correlated with cumulative training days—though interestingly, these markers remained relatively stable during the initial four months of renewed training. The findings suggest that aspartate aminotransferase serves as a useful indicator of both acute muscle trauma from unaccustomed exercise and chronic muscle damage from cumulative training load, with gamma-glutamyl transferase appearing particularly sensitive to overall training volume. For practitioners managing racehorses, these baseline enzyme elevations represent normal physiological adaptation rather than pathology, but tracking individual longitudinal trends—particularly in young horses and during periods of increased training intensity—may help distinguish pathological muscle damage from expected training-induced changes.
Read the full abstract on PubMed
Practical Takeaways
- •Baseline serum AST and GGT levels are higher in fit racehorses; use training status as context when interpreting enzyme results
- •Young horses beginning unaccustomed training show progressive AST elevation over first four months; monitor enzyme trends rather than single values to assess training stress
- •GGT correlates with cumulative training load and may be a useful marker for detecting excessive training stress in racing programs
Key Findings
- •Serum AST and GGT activities were significantly higher in fit racehorses (n=47) compared with sedentary horses (n=57) at baseline (P<0.05)
- •Monthly serum AST in two-year-old racehorses increased significantly from month 1 to 4 during unaccustomed training (P<0.05)
- •AST and GGT showed linear increase with cumulative training days over seven months in previously trained three-year-olds (P<0.05), but minimal increase in first four months
- •Mild to moderate AST elevations in racehorses are associated with cumulative muscle damage from training or trauma from unaccustomed exercise