Diurnal Variations in Blood Cortisol in the Dairy Cow

Abstract
Concentrations of adrenal corticosteroids in plasma were determined by a competitive protein-binding technique in blood samples taken hourly over 24 h from four dairy cows, each sampled for three 24 h periods. Mean blood cortisol was 7.9 ng/ml. Statistical analysis revealed no diurnal variation. Reasons for this are postulated.