Factors influencing pre-race serum concentration of total carbon dioxide in Thoroughbred horses racing in California.
Authors: Cohen N D, Stanley S D, Arthur R M, Wang N
Journal: Equine veterinary journal
Summary
# Editorial Summary: Pre-race Total Carbon Dioxide Levels in Thoroughbreds Racing jurisdictions commonly use pre-race serum total carbon dioxide (TCO2) concentration as a regulatory marker, yet the factors driving variation in this parameter had never been systematically investigated until Cohen and colleagues examined 5,028 race starts across 2,349 Thoroughbreds trained by 287 trainers at California racetracks during 2005. Using mixed-effects modelling to account for both trainer and individual horse effects, the researchers identified several significant associations: horses racing at longer distances, lower race classes, mares, and those receiving furosemide demonstrated lower TCO2 concentrations, whilst cloudy weather conditions were also associated with reduced values. Perhaps most notably, horses finishing in the top three positions had TCO2 concentrations approximately 0.2 mmol/L higher than those finishing outside the placings, and trainer identity itself significantly influenced pre-race TCO2 levels. Although statistically robust, the effect size between superior performance and elevated TCO2 is modest, suggesting that monitoring programmes should recognise the substantial influence of race conditions, horse characteristics, and training practices rather than interpreting TCO2 values in isolation as predictive markers of performance or as reliable indicators of preparation status.
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Practical Takeaways
- •Pre-race TCO2 concentration is influenced by multiple factors beyond horse physiology (weather, race conditions, trainer practices), so single-value thresholds for regulatory compliance may not be fair or scientifically valid
- •Horses with better racing performance tend to have slightly higher TCO2 levels, but the effect size is small and should not be overinterpreted as a performance indicator
- •Trainer management and administration practices (including furosemide use) significantly affect TCO2 values, suggesting standardization of pre-race procedures and timing could improve regulatory testing validity
Key Findings
- •Sex, race class, race distance, furosemide administration, and cloudy weather were significantly associated with pre-race TCO2 concentration (P<0.001)
- •Horses finishing in top 3 positions had TCO2 values 0.2 mmol/L higher than non-placers (P<0.001)
- •Trainer effects were significant contributors to pre-race TCO2 concentration variation
- •Multiple factors influence pre-race TCO2; regulatory monitoring programs should account for these confounding variables