ADMINISTRATION OF PORCINE SOMATOTROPIN BY SUSTAINED-RELEASE IMPLANT -GROWTH-FACTOR AND METABOLIC RESPONSES IN CROSSBRED WHITE AND GENETICALLY LEAN AND OBESE BOARS AND GILTS

Differences in endocrine and metabolic responses to porcine somatotrop in administered by daily injection or sustained-release implant (pST-S R) have been previously observed in genetically lean and obese,gilts a nd barrows. The current study extended those findings by examining res ponses to pST-SR in gilts and boars of a contemporary crossbred line, as well as lean and obese lines. Pigs were treated with 0, 1, or 2 pST -SR implants inserted subcutaneously behind the ear. The osmotically d riven pST-SR implants delivered 2 mg of recombinant pST/d. Pigs were b led on d 0, 7, 14, 28, and 42 after implantation. Sera were assayed fo r pST, insulin-like growth factor (IGF)-I, IGF-II, IGF-binding protein -2 (IGFBP-2), insulin, glucose, and blood urea nitrogen (BUN). Circula ting pST concentrations were increased in a dose-dependent manner (P < .001) in the pST-SR treated pigs, but remained elevated (P <.05) only in the 4 mg of pST-SR/d group on d 42. Significant effects of line, do se, time, line x dose, and time x dose were noted for IGF-I. Serum. IG F-I was elevated in a dose-dependent manner over the 42-d period in al l pST-treated swine. Examination of the line x dose x time interaction indicated that the IGF-I response to pST-SR was greatest in the obese line compared with the lean and crossbred lines. Conversely, serum IG F-II responded to pST-SR to the least extent in the obese pigs. Circul ating IGFBP-2 concentrations were reduced by pST-SR, but were not affe cted by line. The BUN concentrations were reduced by pST-SR. An intera ction of line x dose x time (P <.001) indicated that the response was greater in the obese line. Line x dose x time interactions were also n oted for insulin and glucose concentrations, which were elevated by pS T-SR in a dose-response manner in all lines, but to a much greater ext ent in the obese pigs. These data confirm that sex and genotype influe nce the metabolic and endocrine responses to pST-SR, as demonstrated p reviously using daily injections of pST.