Comparison of blood ionized calcium and acid-base variables in samples obtained from different sampling sites in dairy cows.

Ionized calcium (Ca2+) concentrations, pH, blood gas tensions (pCO2 and pO2), base excess (BE), and bicarbonate (HCO3-) concentrations were determined and standard ionized calcium (stCa2+) concentrations were calculated (Ca2+ corrected to pH 7.4) for the blood withdrawn from the jugular vein, the coccygeal vein or coccygeal artery and the milk vein in 29 clinically healthy post-partum dairy cows. The blood withdrawal site had no significant effect on the blood ionized calcium and standard ionized calcium (mean differences among the blood samples varied between 0.01 and 0.05 mmol/l), or on bicarbonate concentrations or base excess. pH, pCO2 and pO2 were significantly lower or higher in samples taken from the coccygeal vein compared to other venous blood samples.