Circadian Variation in Plasma Cortisol and Corticosterone in Pigs and Mares

Abstract

SUMMARY Plasma cortisol and corticosterone concentrations were determined at different times of the day both in pigs and in mares. Samples were collected from pigs via jugular cannulas and from mares via venipuncture. The highest concentrations in pigs were 1.40 μg. of cortisol/100 ml. of plasma and 0.34 μg. of corticosterone/100 ml. of plusma. In mares the highest concentrations were 2.67 μg. of cortisol/100 ml. of plasma and 0.32 μg. of cortico-sterone/100 ml. of plasma. A circadian pattern was observed for cortisol in both species, with peak values occurring during the morning. A similar pattern was observed for corticosterone in mares, but not in pigs.