Total and ionized calcium in parturient dairy cows and their calves.

Ionized Ca in blood, standard ionized Ca, pH, and total Ca in plasma were measured in 33 Holstein-Friesian dairy cows and their calves. Blood was taken immediately postpartum and at 12, 24, 48, and 72 h after calving. Cows and their calves were grouped according to parity. Concentrations of ionized and total Ca consistently were higher in neonates than in the dams. Parity differences were significant for maternal ionized Ca and total Ca. However, parity was not significant for ionized or total Ca in the blood of corresponding calves. Changes in ionized Ca concentration in calves of first lactation cows largely were attributable to perinatal acidosis. In contrast to total Ca concentrations, the ionized Ca and standard ionized Ca concentrations in dams and calves were relatively stable throughout the study, suggesting that ionized Ca concentration in blood is indicative of the Ca status of the dairy animal.