Factors influencing pre-race serum concentration of total carbon dioxide in Thoroughbred horses racing in California

REASONS FOR PERFORMING STUDY: Many racing jurisdictions monitor pre-race serum concentration of total carbon dioxide (TCO2) among racing horses. To our knowledge, factors influencing concentration of TCO2 among horses participating in racing have not been systematically evaluated and reported. OBJECTIVES: To determine if characteristics of horses and racing conditions routinely recorded were significantly associated with pre-race concentration of TCO2, while accounting for and estimating effects of trainer and horse. METHODS: Pre-race serum TCO2 concentrations from 5028 starts made by 2,349 horses trained by 287 trainers at 2 racetracks in California during 2005 were examined. Data regarding characteristics of starters and race conditions obtained from a commercial database were recorded for each start. Data were analysed using mixed-effects, with TCO2 concentration as the dependent variable, and trainer and horse nested within trainer as random effects. RESULTS: Sex, class and distance of race, frusemide administration and cloudy weather conditions were significantly (P<0.001) associated with pre-race TCO2 concentration. Horses that finished in the top 3 positions had values that were slightly (0.2 mmol/) but significantly (P<0.001) greater than horses not finishing in the top 3. There were significant effects of trainer on pre-race TCO2 concentration. CONCLUSIONS: A variety of factors may influence pre-race TCO2 concentration in horses. Horses with better performance tend to have higher pre-race TCO2 concentrations. POTENTIAL RELEVANCE: TCO2 concentration is associated with improved performance although the magnitude of effect was quite small. Regulatory programmes based on monitoring should consider the influence of other factors on TCO2 concentration.