Responses to administration of growth hormone releasing hormone and glucose in steers receiving stair-step and extended restriction on feeding

In this study, we assessed the temporal response of growth hormone (GH)/ghrelin to the intravenous administration of GH releasing hormone (GHRH) in 11- (period 1) and 15-month-old (period 2) Korean native steers, as well as the insulin induction response to glucose administration after completion of the feeding scheme in 11-month-old Korean native steers experiencing stair-step and extended restriction feeding schemes. The experiment was divided into periods 1, 2, 3, and 4 with durations of 3, 2, 4, and 2 months, respectively. The control group (n=9) was fed according to a standard feeding program during all 4 periods. The T1 (n=9; stair-step fed group) was fed a diet with total digestible nutrients (TDN) at concentrations 20% less and more than the TDN concentration fed to the control group in periods 1 and 3 and periods 2 and 4, respectively, whereas the T2 (n=9; extended restricted group) was fed increasing levels of TDN, having concentrations of 30%, 20%, 10% less than and 20% more than the TDN concentration of control group, during periods 1, 2, 3, and 4, respectively. Randomly chosen steers (n=4, total 12 heads) from the C, T1, and T2 groups were used for the experiment of GHRH and glucose administration. Compared to the control group, the T1 showed elevated levels of plasma GH and insulin after GHRH and glucose administration (p<0.05) and significantly greater body weight gain and feed efficiency. Although the total amounts of ghrelin in plasma were significantly decreased in the T1 group after GHRH administration (p<0.05), GHRH treatment did not affect the acyl ghrelin concentration in the plasma during compensatory growth. The results illustrate that stair-step feeding can promote growth performance by altering the endocrine responses associated with energy utilization, such as the production of GH, ghrelin, and insulin, in steers.