Ghrelin affects not only growth hormone secretion but also nutrient utilization and metabolic hormone secretion in humans and experimental
animals. The effects of ghrelin on plasma metabolic hormone and metabolite levels in domestic herbivores remain unclear despite the fact that the
physiological characteristics of nutrient digestion and absorption imply specific responses to ghrelin. Therefore, the effects of ghrelin on plasma
glucose, pancreatic hormones and cortisol concentrations were investigated in Holstein dairy cattle in various physiological states. Ghrelin (0.3
nmol/kg) or placebo (2% bovine serum albumin in saline) was intravenously injected in pre-ruminant calves (pre-rumen function), adult nonlactating
(functional rumen) and lactating cows (functional rumen and lactation), and plasma glucose, insulin, glucagon and cortisol concentrations
were then determined. Ghrelin injection increased plasma glucose concentrations in adult cows, especially in lactating cows. No hyperglycemic
response was observed in pre-ruminant calves. A transient rise of insulin and glucagon levels was distinctively found in lactating cows in response
to the ghrelin administration. Ghrelin injection decreased the insulin level in pre-ruminant calves. Ghrelin increased cortisol secretion
independently of the physiological state. The results of the present study suggest that the effects of ghrelin on plasma glucose and pancreatic
hormone levels may reflect differences in the physiological states of dairy cattle.