Influence of protein nutrition on the response of growing lambs to exogenous bovine growth hormone

Abstract

ABSTRACT Interactions between protein supply and the anabolic response to exogenous bovine (b) GH have been examined in two experiments using 28–35 kg lambs sustained entirely by intragastric infusion of volatile fatty acids (700 kJ/kg W0·75 per day) into the rumen and the casein (600 mg (low protein; LP) or 1200 mg (high protein; HP)/kg W0·75 per day) into the abomasum. Sheep received continuous i.v. infusions of bGH for 6 days in experiment 1 and for 18 days in experiment 2. Nitrogen balances were determined daily throughout both experiments and blood samples, from indwelling catheters, were assayed for GH, insulin-like growth factor-I (IGF-I), insulin and glucose. Infusion of bGH increased plasma GH concentration by five- to sixfold in all animals. There was an increase in N retention in both HP and LP animals over the first 2–3 days of GH administration. HP animals sustained higher N retentions (31%; P < 0·05) throughout the GH administration but LP animals did not. In contrast, plasma IGF-I concentrations increased progressively over the first 72 to 96 h of GH administration in all sheep and thereafter remained significantly (P < 0·05) elevated until termination of the GH infusion. In lambs which received both HP and LP infusions in experiment 1 the increase in IGF-I concentration by day 6 of GH administration was significantly (P < 0·05) greater when they received the higher protein intake. Plasma insulin concentrations increased rapidly (P < 0·05) with the onset of GH administration to levels which were 2·5 (LP)- and 4·8 (HP)-fold greater than those observed in the pre-and post-GH periods. Glucose concentration also increased during GH administration (P < 0·05), by 35% in LP animals and by 58% in HP animals. High protein availability appeared necessary to sustain a protein anabolic response where lambs received exogenous GH infusions, even though plasma IGF-I concentrations were elevated on both high and low protein treatments. Journal of Endocrinology (1991) 130, 53–61