Effect of melatonin and lighting schedule on energy metabolism in broiler chickens

The effect of melatonin and lighting schedule on energy metabolism in broil er chickens was studied. Eight groups of six female broiler chickens each w ere assigned to a continuous lighting schedule [23 h light (L):1 h darkness (D)] or an intermittent lighting schedule (1L:3D), and were fed a diet wit h or without melatonin (40 ppm). At 21 d of age, the chickens were placed i n respiration chambers for 20 d. Energy and nitrogen balances, heat product ion, and physical activity were measured per group. The only effect of mela tonin on energy metabolism, was a decreasing effect on activity-related hea t production. The intermittent lighting schedule induced improved feed conv ersion, higher metabolizability of the diet, and lower physical activity co mpared to continuous lighting. No interactions between melatonin and lighti ng schedule were found on energy metabolism traits. Lighting schedule stron gly affected daily heat production pattern (total, activity-related, and no nactivity-related heat production). Melatonin had a reducing effect on acti vity-related heat production during the day, especially during light period s. The present study demonstrated that reduced energy expenditure for physi cal activity, caused by the supplementation of melatonin to the diet, might be a reason for the often observed improvement of feed conversion. Further more, this study showed that feed conversion was improved with an intermitt ent lighting schedule, which was related to higher metabolizability and low er energy expenditure on physical activity, compared to continuous lighting .