Total Carbon Dioxide (TCO₂) Concentrations in Thoroughbred and Quarter Racehorses in Louisiana

The TCO₂ (total carbon dioxide) test is performed on the blood of racehorses as a means of combatting the practice of administering alkalizing agents. This study evaluated serum TCO₂ concentrations and factors influencing concentration of TCO₂ in Thoroughbred and Quarter Horses. The normality of data were evaluated with a Shapiro-Wilk test. Mann-Whitney tests and Kruskal-Wallis tests were used against different effects. When a fixed effect was detected, Dunn's post-hoc comparisons were performed. The median pre-race serum TCO₂ concentration (32.20 mmol/L (interquartile range (IQR): 30.80-33.50)) was higher than that of post-race samples (26.70 mmol/L (IQR: 24.55-29.25)) (P < .0001). The median TCO₂ concentrations in pre-race samples were different between Thoroughbred (32.40 mmol/L (IQR: 30.90-33.60)) and Quarter Horses (31.30 mmol/L (IQR: 30.00-32.50)) (P < .0001). The median pre-race TCO₂ concentrations were 32.75 (IQR: 31.40-33.90), 31.40 (IQR: 29.80-32.80), 32.50 (IQR: 31.20-33.88), and 31.60 (IQR 30.00-32.70) mmol/L in racehorses at Fair Grounds, Louisiana Downs, Delta Downs, and Evangeline Downs racetracks, respectively (P < .0001). The total serum TCO₂ concentrations in Thoroughbred and Quarter Horse racehorses were affected by seasonal temperature variation (P < .0001). A smaller sample size was available for post-race samples (n = 205) and Quarter Horse pre-race samples (n = 351). The results of this study indicated that the breed, seasonal temperature variation, pre-race or post-race sampling, and track location are strongly correlated to total TCO₂ concentrations. It was not clear whether the statistically significant differences in TCO₂ levels among racetracks in Louisiana were due to location of racetracks and/or seasonal temperature variation.