SOMATOTROPIN ENHANCES THE RATE OF AMINO-ACID DEPOSITION BUT HAS MINIMAL IMPACT ON AMINO-ACID BALANCE IN GROWING PIGS

This experiment was conducted to establish the influence of porcine somatotropin on tissue distribution and deposition rates of amino acids in growing pigs. Barrows were treated daily with buffer or porcine somatotropin (100 mu/kg body wt) when they weighed between 30 and 64 kg (eight pigs/group). Pigs were restrictively fed so that the average food intake was 1.86 kg/d. The corn-soybean meal-skim milk-based diet contained 18% crude protein and 1.2% lysine, and was designed to meet muscle amino acid ratio profile with respect to lysine as the first limiting amino acid for growth. Tissue levels of eighteen amino acids were determined on lyophilized samples that were appropriately hydrolyzed and analyzed by HPLC. The concentrations (mg/g dry wt) of all amino acids were greater in carcass, skin, head and empty body of porcine somatotropin-treated pigs; amino acid concentration in viscera was not influenced by porcine somatotropin. However, when the concentration of each amino acid was expressed on a per unit protein basis, the amino acid profiles of control and porcine somatotropin-treated pigs were quite similar. The average deposition rate of each amino acid was increased similar to 67% by porcine somatotropin. When the deposition of each amino acid was calculated in relation to lysine, however, the pattern of amino acid utilization for growth was similar for control and porcine somatotropin-treated pigs; exceptions were arginine, glycine and tryptophan. The ratio of indispensable to dispensable amino acids that were deposited was also similar for control and porcine somatotropin-treated pigs. These data indicate that the synthesis rate of individual proteins can be influenced by porcine somatotropin, but the balance of amino acids remains largely unaffected, suggesting that the changes in protein and amino acid metabolism elicited by porcine somatotropin are consistent with normal growth processes.