Effects of dietary melatonin on broiler chicken exposed to continuous lighting during the first two weeks of life

Intensive broiler chicken production involves different lighting regimes, which affects a natural cycle of secretion of melatonin, a hormone included in multiple physiological processes in a bird's body. This research aimed to determine the effects of dietary melatonin supplementation during the first two weeks of broiler chickens' life, bred under constant 24 h lighting, on their health and some hematological, biochemical, and production parameters. The study lasted 6 weeks. Three hundred and twenty 1-day chickens were divided into two groups (control - C and experimental - M), with four replications and 40 chickens in each replica. In the first two weeks (the first phase of the study), a continuous lighting mode 24L: 0D was applied. Group M was receiving a diet supplemented with 30 mg/kg synthetic melatonin only during the first phase. Group C had a diet without melatonin supplementation throughout the whole study. Melatonin addition had a statistically significant effect (P<0.01) on the mean values of body weight and daily weight gain at the end of the 1st, 2nd, 3rd, 4th, 5th, and 6th week. The chickens of the experimental group have had a significantly higher value of the European Production Efficiency Factor (EPEF) (P