Detection of bicarbonate administration (milkshake) in Standardbred horses

SUMMARY Total plasma carbon dioxide (TCO₂) concentrations were measured in Standardbred horses to determine criteria to discriminate between normal horses and horses with excessive TCO₂ concentrations on raceday. TCO₂ concentrations from stabled horses were distributed normally with a mean of 30.2 mmol/L and a standard deviation of 1.2 (n = 192) while pre-race TCO₂ concentrations were not normally distributed. The results indicate that about 50 horses per million are likely to have TCO₂ concentrations greater than or equal to 35 mmol/L and that it is extremely unlikely that a normal horse would have a resting TCO₂ concentration above 36 mmol/L. These values were associated with sensitivities of 67% and 59%, respectively, and with a specificity of 100%. TCO₂ concentrations were relatively stable in blood samples stored at 4°C for 4 days, whereas the TCO₂ in specimens stored at room temperature (25°C) and at ambient temperature (16–28°C) declined progressively over 5 days. The accuracy and precision of the Beckman EL-ISE Auto Analyser were acceptable and within the manufacturers specified range. Paired specimens analysed using a Beckman EL-ISE Auto Analyser and a Kodak Dry Chemistry Analyser were not significantly different. However, the measurements made using the Kodak Dry Chemistry Analyser averaged 0.5 mmol/L higher than those analysed on the Beckman EL-ISE. The significance of these sources of variation in TCO₂ concentration in relation to the testing of horses for ‘milkshake’ administration are discussed.