|Buonomo F C, - MONSANTO AGRIC COMPANY|
|Yen J T,|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 28, 1994
Publication Date: N/A
Interpretive Summary: The present study examined the endocrine and metabolite responses of boars and gilts of a commercial type crossbred line and genetically lean and obese lines to the sustained release form of pST administration. Efficiency of production of marketable pork is improved with pST administration. The pigs used in the study represent a broad sampling of normal growth characteristics and endogenous endocrine secretion. Circulating concentrations of pST were increased with increased pST administration. Circulating concentrations of pST peaked at day 7 and then declined, but at 6 weeks pST concentrations in pigs receiving the higher dose were still above levels in control pigs. Serum concentrations of insulin-like growth factors (IGF) I and II, insulin and glucose were also increased with increasing dose of pST administered. Serum levels of IGF binding protein and urea nitrogen were decreased with increasing dose of pST. The changes in IGF-I, glucose, insulin and urea nitrogen were greatest in the obese line pigs. While most endocrine and metabolite measures were influenced by genotype (crossbred vs lean vs obese), they were not influenced by sex (boar vs gilt). In contrast, most measures of growth and carcass composition in these pigs administered pST were influenced by sex. Influence of sex on growth and composition may be the consequence of sexual differentiation expressed through differential response to rather than differential secretion of endocrine growth factors.
Technical Abstract: The current study extended previous findings by examining responses to porcine somatotropin administered by sustained release implant (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 delivering 2 mg pST/d and were bled on d 0, 7, 14, 28 and 42 post-implantation. Circulating pST levels were increased in a dose dependent manner in the pST- SR treated pigs, but remained elevated only in the 4 mg pST-SR/d group on d 42. Significant effects of line x dose and time x dose were noted for IGF-I. Serum IGF-I was elevated in a dose- dependent manner over the 42 d period in all pST-treated swine. IGF-I response to pST-SR was greatest in the obese line as compared to the lean and crossbred lines. Conversely, serum IGF- II responded to pST-SR to the least extent in the obese pigs. Circulating IGFBP-2 levels were reduced by pST-SR, but not affected by line. BUN levels were reduced by pST-SR; the response was greater in the obese line. Line x dose x time interactions were also noted for insulin and glucose concentrations, which were significantly elevated by pST-SR in a dose-responsive manner in all lines, but to a much greater extent in the obese pigs. These data confirm that sex and genotype influence the metabolic and endocrine responses to pST-SR, as demonstrated previously using daily pST injections.