Plasma corticosterone in chicks reared under several lighting schedules

Area of Science:

• Animal Physiology
• Endocrinology
• Chronobiology

Background:

• The regulation of plasma corticosterone levels is crucial for broiler chick health and development.
• Lighting regimes are known to influence physiological processes in poultry.
• Understanding the interplay between light, circadian rhythms, and stress hormones is essential for optimizing poultry welfare.

Purpose of the Study:

• To investigate the impact of different lighting regimes on plasma corticosterone levels in broiler chicks.
• To determine the presence and characteristics of a diurnal corticosterone rhythm under various light conditions.
• To assess the influence of light intensity and sampling time on corticosterone levels.

Main Methods:

• Plasma corticosterone was measured using radioimmunoassay in male broiler chicks (6-7 weeks old).
• Chicks were reared under controlled lighting regimes, including darkness, diurnal light, and continuous light.
• Around-the-clock blood sampling was performed to analyze diurnal rhythms.

Main Results:

• Chicks reared in darkness exhibited significantly lower plasma corticosterone than diurnal or continuous light groups.
• A clear diurnal rhythm of corticosterone was observed, with higher levels during the day and lower levels at night.
• This diurnal rhythm persisted in constant light, though it appeared phase-shifted or free-running.

Conclusions:

• Photoperiod significantly influences plasma corticosterone levels in broiler chicks, with darkness leading to suppression.
• Broiler chicks possess an endogenous diurnal corticosterone rhythm that is robust and can persist under constant light.
• Light intensity and the specific light status (on/off) at the time of sampling did not significantly affect corticosterone levels in this study.