Intensive production practices, faulty maintenance and feeding, unsuitable keeping conditions, antinutritional factors in feeds and similar abnormalities lead to irregularities in both hormone and enzyme systems in poultry. Especially, due to disorders in endocrine system, a specific hormone, melatonin, can not be produced or underproduced, and thus its metabolic and physiological functions are negatively affected in the organisms. Melatonin (ML) is one of the important hormones that prevent

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... abolic and physiological disorders in poultry but does not attract attention by poultry scientist. ML regulates the brain's biological clock, acts on respiration, circulation, excretion, reproduction and immunity system. ML helps regulate feed consumption, energy metabolism and body heat. It also provides elimination of free radicals in the body. ML stimulates growth hormone secretion and, thus, effects growth performance of poultry positively. It is considered necesary to focus more effectively on the melatonin hormone, which is a positive contribution to animal welfare by correcting metabolic-physiological disorders in poultry. In this review, the definition of melatonin, its interaction with other hormones, its effect on the physiological and metabolic functions of poultry were examined.