[The ionized calcium in the blood of domestic chickens: dependence on age and sex].

In the present study concentration of ionized calcium and the correlation between total and ionized calcium in blood of domestic fowl and its dependence on age and sex were investigated. Furthermore a possible influence of blood sampling procedure on the measured values was assessed. Leghorn chickens of either sex, aged 3, 9, 25, and 80 weeks, respectively, were used. Blood sampling was performed by vein-puncture and indwelling catheters, respectively, of both ulnaris vein and artery of animals which had been fasting for 12 hours. Determinations of ionized calcium concentration was carried out by use of an ion-selective electrode (ICA1), and of total calcium concentration in plasma using atomic absorption, respectively. After attainment of sexual maturity total calcium in roosters rose from 2.73 to 2.85 mmol/l, whereas ionized calcium fell from 1.45 to 1.40 mmol/l and per cent fraction of ionized/total calcium (extent of ionization) from 53.1 to 49.1%, respectively. After attainment of sexual maturity in hens, the content of total calcium in venous blood rose from 2.78 to 5.78 mmol/l, and of ionized calcium from 1.45 to 1.59 mmol/l, respectively, whereas the extent of ionization was significantly reduced from 52.2 to 27.1%. On comparison of the vein-puncture and indwelling catheter technique a marked influence of the blood sampling procedure on calcium concentrations measured in blood of chicken became evident. On attainment of sexual maturity both the arterial and the venous blood (sampled from indwelling catheters) of hens showed levels of ionized calcium about 8% higher as compared to roosters. The extent of ionization amounted to 39% in sexually mature females as opposed to 51% in males. Concentrations of calcium ions in venous blood averaged 0.07 to 0.08 mmol/l higher compared to arterial blood in either sex. Concentration of ionized calcium did not exhibit any correlation to total calcium in adult animals. However, the concentration of ionized calcium was inversely correlated to blood pH.