Studies on Blood Calcium Relationships in the Turkey

Studies were conducted to establish normal ionized calcium levels and the relationship of ionized calcium to total blood calcium concentrations during various physiological states in the turkey. Ionized calcium levels were similar in fresh plasma and serum. Ionized calcium in plasma was significantly lower after 8 hr of storage at 4 C compared to fresh plasma. After only 4 hr of storage ionized calcium levels were significantly depressed in serum. Significant changes were noted in both plasma and serum ionized calcium when stored frozen or unfrozen for 24 hr. Several anticoagulants were tested for interference with plasma free calcium. Sodium heparin, 10 U/ml, was found to be the most suitable. In the poult, plasma ionized calcium was 35% of total calcium and was influenced by a withholding food and refeeding regimen. Absolute ionized calcium concentrations were greater in the blood plasma of adult hen but comprised a smaller proportion of total calcium (12 to 24%) compared to poults or age-matched males. It is apparent from the results of this study that dramatic changes in total blood calcium concentrations do not result in similar magnitude fluctuations of ionized calcium concentrations; however, the relationships of ionized to total calcium would be the best index to relate calcium homeostasis and physiological state.