response of plasma leptin and feed intake to growth hormone administration in Holstein calves with different planes of nutrition

This study was conducted to observe the effect of the growth hormone (GH)/insulin-like growth factor-1(/IGF-1) axis on leptin and feed intake of 15 Holstein calves in three groups. One group was fed a normal diet (control); the second group, with high nutrition after low feeding with bovine growth hormone (bGH), and a third group, without high nutrition (saline) after low feeding. Each group was intramuscularly (i.m.) injected daily with bovine GH (200 microgram kg(-1) d(-1)) or saline solution for 10 d. No significant differences were found in the concentrations of plasma leptin over time for a 24-h period. Plasma leptin was decreased in both saline and GH groups during low and high nutrition regimes, respectively, while IGF-1 levels increased for both nutrition regimes (P < 0.05). With GH treatment during refeeding periods (P < 0.05), leptin levels increased and feed intake decreased; however, the plasma leptin levels slightly decreased with GH treatment during low feeding periods. The plasma IGF-1 concentration increased with GH administration during normal and refeeding periods (P < 0.05). These results indicate that the response of plasma leptin levels to GH varied according to the nutritional condition. In addition, the GH/IGF-1-induced increase in leptin production during the refeeding period may serve as a signal to reduce the feed intake or to increase dramatically after feed restriction in cattle.