Advances in the Manipulation of Pig Growth

Two experiments involving a total of 132 entire male pigs were conducted to investigate the interrelationships between exogenous porcine growth hormone (pGH) administration (0 and 0.09mg recombinant pGH/kg/d) and dietary ideal protein levels ranging from 83 to 238 and 70 to 238g/kg on the performance and carcass composition of pigs growing from 30 to 60kg (Experiment 1) and 60 to 90kg (Experiment 2) respectively. Growth rate and feed:gain improved with increasing dietary ideal protein up to approximately 173 and 137g/kg in experiments 1 and 2 respectively and were enhanced by pGH administration in pigs offered the higher protein diets but unaffected or slightly depressed by pGH administration to pigs given the two lowest protein diets in each experiment. Protein deposition and plasma Insulin like growth factor -1 levels were similarly increased by pGH administration to pigs given the four higher protein diets in Experiment 1 but unaffected by pGH in pigs given the two lowest protein diets (83 and 114g/kg). In contrast fat deposition and carcass fat content in experiment 1 and carcass P2 fat thickness at 90kg in experiment 2 declined with increasing dietary protein and were reduced on all dietary treatments by pGH administration. These results demonstrate independent actions of GH on protein and lipid metabolism and suggest that the stimulation of protein accretion by GH is mediated via IGF-1, the release and (or) synthesis of which appears to be inhibited by dietary protein (amino acid) deficiency.