Concentrations of free (Ionized) and total calcium and magnesium in healthy captive Asian Elephants (Elephas maximus) and effects of sample type and pH on measured free calcium and magnesium concentrations

The Asian elephant (Elephas maximus) is an endangered species, with an overall low reproduction rate in captivity, and a long, 22-month gestation, mostly with a single calve. Calcium and magnesium are important for the normal progression of gestation and parturition. This study measured blood total and ionized calcium (tCa and iCa, respectively) and total and ionized magnesium (tMg and iMg, respectively) in four healthy, captive Asian elephant cows in the Tisch Family Zoological Gardens, Jerusalem, every alternative month, over a 1-year period, to establish their reference intervals and examine sample pH and sample type effects on measured iCa and iMg concentrations. iCa and iMg were measured using an ion-selective electrode electrolyte analyzer. Calcium and magnesium levels in diet samples were measured. The iCa:tCa and iMg:tMg ratios were 0.44 and 0.73, respectively. Mean iMg concentrations in whole-blood, heparinized plasma and serum were 0.58, 0.65 and 0.66 mmol/L, respectively. iCa and iMg concentrations in the three sample types were highly correlated, with no sample type effect on measured iCa concentration, but significant effect on iMg concentration, with significantly lower whole-blood levels vs. serum and plasma. Serum albumin and both tCa and tMg concentrations positively correlated. Sample pH had no effect on measured iCa or iMg levels. This study is the first to measure iMg in Asian elephants, and assess the effects of sample type and pH on the results. It was concluded that different iMg reference intervals should be established for each sample type.