In birds, exogenous melatonin possesses a wide spectrum of biological effects and can interfere with a wide range of behavioral and physiological processes including growth but the underlying mechanisms under feed restriction conditions have not been well defined. This study was carried out to investigate the effects of melatonin on growth performance, gut health, and some biochemical parameters of broilers subjected to feed restriction.Eleven-day-old male Ross 308 broilers were randomly distributed to 3 dietary treatments with 6 replicates of sixteen chicks each as follows: (1) control (CON); (2) 20% feed restriction (d 11 –18; FR); and (3) the same as FR group, but melatonin was supplemented to drinking water (30 m g/ml, d 11–35; MFR). All birds had access to feed and water from 18 to 35 d of age. At d 35, broilers were sampled for quantification of blood components, intestinal morphology, and microbial counts. Supplementation of melatonin improved feed conversion rate of feed restricted birds (P o 0.05). The MFR group had higher plasma growth hormone level as compared with CON (Po 0.05). The villus height of duodenum was increased in MFR group as compared with those of CON and FR groups ( P o 0.05). Melatonin supplementation increased the jejunal villus height of chickens in FR group (P o 0.05).Compared to FR group, ileal coliform counts decreased in birds treated with melatonin and CON group (P o 0.05 and o 0.01, respectively). An increment in ileal Lactobacillus counts was found in MFR group compared to CON (P o 0.05). No significant differences were noticed in microbial counts of cecum among treatments. Results revealed that administra-tion of melatonin to chickens seems to improve performance, gut histomorphology, and microbiota under temporarily feed restriction conditions.

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