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Title: ADMINISTRATION OF PORCINE SOMATOTROPIN BY DAILY INJECTION: GROWTH AND ENDOCRINE RESPONSES IN GENETICALLY LEAN AND OBESE BARROWS AND GILTS

Author
item KLINDT J - 5438-01-07
item BUONOMO F C - MONSANTO AGRICULTURAL CO.
item YEN J T - 5438-01-07
item POND W G - 6250-00-00
item MERSMANN H J - 6250-00-00

Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/26/1995
Publication Date: N/A
Citation: N/A

Interpretive Summary: Excessive fat production is a concern of the pork industry. Administration of porcine somatotropin (pST) is among methods proposed to reduce unwanted fat. The present study examined the growth, carcass, metabolite, and endocrine responses of genetically lean and obese barrows and gilts, pigs with very different growth characteristics, to pST administered at doses of f0, 2, and 4 mg/d by daily injection for 6 weeks. Administration of pST resulted in decreased feed intake, increased rate and efficiency of gain and decreased rate of backfat deposition. The carcasses of pigs which were administered pST contained more marketable lean pork (quantity of trimmed primal cuts) and less fat. These changes in growth occurred in both lines and sexes, however, the growth performance and carcass merit of the pST-treated pigs still reflected their genotype and sex. The greater production of trimmed primal cuts by obese barrows administered 4 mg pST/d than by untreated lean barrows is evidence of the efficacy of pST. Administration of pST may allow use of maternal lines which exhibit superior reproduction and less than superior growth and carcass characteristics, and superior terminal sire lines to achieve optimal efficiency of pork production.

Technical Abstract: Influences of genotype and sex on responses to porcine somatotropin (pST) administered by daily injection were examined in genetically lean and obese gilts and barrows. Doses of 0, 2, and 4 mg/d of pST were administered by daily injection for 6 wk. Pigs were individually penned with ad lib feed. Blood was collected at various times during the trial for measurement of pST, insulin-like growth factor (IGF) -I, IGF-II, insulin, glucose, urea nitrogen, nonesterified fatty acids (NEFA) and triglycerides. Somatotropin induced dose-dependent decreases in feed intake, while gain and efficiency of gain was increased in a quadratic manner indicating that the optimal dose was approached at 4 mg pST/d. Effects of sex and line were noted for feed intake, gain, efficiency and rate of backfat deposition. Quantity of lean and bone in the ham was increased and that of fat decreased with dose of pST. Many organ and carcass measures were influenced by line and sex. Throughout the trial pST induced increases in serum levels of IGF-I, -II, insulin and glucose and decreases in urea nitrogen. Serum pST was effected by line and sex, suggesting influence of line and sex on clearance. Serum pST in pigs which received pST about 24 h after injection was lower than in control pigs indicating negative feedback on endogenous secretion of pST. The increase in insulin, IGF-I and IGF-II and decrease in urea nitrogen were evident at 24 h after the initial injection. Hyperglycemia was detected only in pigs receiving 4 mg pST at 24 h. While pST improves the growth and carcass measures in genetically lean and obese barrows and gilts, the influences of line and sex are not expunged by exogenous administration of pST.