Daily variation of corticosterone and thyroid hormones in broiler cockerels

An experiment was conducted to monitor fluctuations in the major adrenal steroid, corticosterone (B), and two iodinated thyroid hormones, triiodothyronine (T3) and thyroxine (T4), over the course of a 24-hr day in broiler cockerels. A circadian variation was observed in B concentrations with the highest found at 0130 hr (23 hr light: 1 hr darkness; photophase beginning at 0100 hr). No circadian variation was observed for either T3 or T4.