EFFECT OF PORCINE SOMATOTROPIN ADMINISTRATION IN YOUNG-PIGS DURING THE GROWTH-PHASE FROM 10 TO 25 KILOGRAMS

We conducted two experiments to determine the efficacy of exogenous po rcine somatotropin (pST) on enhancing performance during an early phas e of growth (10 kg initial BW) when pigs are already growing efficient ly and have high rates of lean deposition and low rates of lipid depos ition. In Exp. 1, performance was measured on 45 barrows that received one of five daily doses (0, 50, 100, 150 and 200 mu g/kg BW) of recom binant pST. In Exp. 2, 27 barrows were used in a slaughter-balance stu dy in which two groups received daily either buffer (control) or 120 m u g/kg BW of pST and the third group was slaughtered for initial body composition. In both experiments, pigs received daily i.m. injections of their respective dose for 20 d. The diet was fed for ad libitum con sumption and calculated to contain 3.5 Meal DE/kg, 22.3% CP, and 1.5% lysine. Administration of pST failed to alter overall growth rate or e fficiency of gain in either experiment. However, in Exp. 2 pigs treate d with pST had increased deposition rates of protein and water but red uced lipid deposition rates. Furthermore, pST treatment resulted in ch aracteristic reductions in plasma urea nitrogen and elevations in gluc ose and NEFA. Plasma concentrations of insulin and IGF-I were also inc reased, but pST reduced IGF-II and IGF binding protein-a. Overall, the data demonstrated that very young pigs respond to pST with enhanced l ean tissue accretion and metabolic changes, but the response is attenu ated compared with previous studies in older growing pigs.