Plasma Corticoid Levels During Early Postnatal Life in Calves 1

Abstract

There do not appear to be data available on plasma levels of aldosterone and progesterone in the newborn calf. Previous studies on plasma corticoid concentration in the neonate of this species have been confined to the measurement of 17-hydroxycorticosteroids (1-4). In addition, evidence as to whether the calf is born with an adequate or poor supply of circulating adrenocorticoids is controversial. In this regard, several studies (2-4) have shown in normal neonatal calves that plasma cortisol levels vary with age, with the highest concentration seen during the first day following birth. Furthermore, these data (2-4) indicated that the initial high levels of plasma cortisol decreased toward the adult concentration within the next few days. Moll (5), however, favors the view that calves are born with immature adrenals and thus are poorly equipped to cope with environmental changes. There is also disagreement as to whether corticosterone is present in plasma at birth (2, 6). The present study was, therefore, designed to determine if the calf has increased plasma corticoid levels at birth, which may contribute to a rapid adaptation to conditions of extra-uterine life.

Materials and methods. Five healthy, male, colostrum-fed dairy calves were utilized. The animals were less than 24 hr old at the start of the trials. They were kept in a room at 22 ± 3° and were fed 1-2 liters of warm milk twice daily after blood collection. Heparinized serial blood samples from catherterized jugular veins were collected at 12-hr intervals. The samples were centrifuged at 14,500g for 20 min, and the plasma was removed and stored at −20° until assayed.

Radioimmunoassays for aldosterone (7) and progesterone (8), and competitive protein-binding assays for cortisol and corticosterone (9) were used for the measurement of these hormones in plasma.