The gut hormone ghrelin plays an important physiological role in modulating GH secretion, insulin secretion and glucose metabolism. To test the hypothesis that long term effect of peripheral ghrelin on serotonin and insulin levels in ruminant species, ten male lambs were 2 months old with an average body weight of 26 kg and 2 groups according to ghrelin. treatment in group I, animals were fed ad libitum in the group II, animals were fed ad libitum and intravenously injected with the ghrelin. In the laboratory, researchers have shown that ghrelin administration was significantly decreased plasma serotonin, insulin and glucose concentrations in the long term. Although, the results obtained by ghrelin. treatment in the long term are not enough clear in ruminant species and further research should validate the obtained results before applying this information on relationships between ghrelin, insulin and serotonin.