Technical Note: Using calcium carbonate as an osmolar control treatment for acid-base studies in horses

The efficacy of using calcium carbonate as an osmolar control treatment for acid-base studies in horses receiving alkalizing compounds was evaluated. Six mares were nasogastrically intubated with isomolar quantities of sodium or calcium as sodium bicarbonate or calcium carbonate or with water during three treatment periods. Doses of the carbonic acid salts were 500 mg/kg sodium bicarbonate mixed with 4 L of distilled water (positive control) and 595 mg/kg calcium carbonate mixed with 2 L of distilled water to yield isoosmolar treatments. Four liters of distilled water served as the negative control. Jugular venous blood samples were drawn before intubation and at hourly intervals for 6 h after intubation. The serum electrolytes Na⁺ and K⁺, blood pH, and HCO₃^- were determined. The sodium bicarbonate treatment increased blood pH and HCO₃^- (P < 0.01) above both the water and CaCO₃ treatments. No differences (P > 0.05) were found between the water and CaCO₃ treatments. These data indicate that calcium carbonate may serve as a suitable osmolar control treatment for studying the effects of treatments that affect acid-base status of horses.