Plasma sodium, potassium and aldosterone levels in newborn calves.

1 Plasma sodium, potassium and aldosterone levels were measured in 11 calves during the first postnatal week. 2 Plasma sodium and potassium levels showed no significant variation between birth and the seventh day of postnatal life. 3 A sharp decrease in plasma aldosterone levels was observed between birth (119 +/- 7 pg/ml) and 12 hrs (25 +/- 8 pg/ml). The lowest values (13 +/- 5 pg/ml, similar to those measured in adult cows) were measured on day 7.