Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/1/1999
Publication Date: N/A
Citation: Interpretive Summary: Growth hormone (GH) has been demonstrated through a number of published studies to improve the carcass composition of swine. This improvement results in a greater amount of lean meat and greatly reduced amount of fat. The present study was performed to determine if withdrawal of treatment reverses the positive effects of GH on carcass composition and metabolic parameters responsible for this reduction in carcass fat. A baseline study demonstrated that 4 weeks of GH treatment improved feed efficiency by 27% and reduced carcass backfat by 43%. The reduction in backfat could be accounted by a 44% reduction in fatty acid metabolism and a 70-86%% reduction in glucose metabolism by the backfat. The second experiment looked at the effect of 7 days of GH treatment and the subsequent withdrawal of GH treatment for 8 days on backfat metabolism. Fat synthesis was reduced by d4 (68%) of GH treatment. Fatty acid synthase, the enzyme responsible for carbohydrate conversion to fat, was reduced by d7 (26%). Fat synthesis increased to control values after GH withdrawal. Blood urea nitrogen, a marker for protein breakdown, was reduced during GH treatment and returned to normal by d4 of withdrawal. The results indicate most of the metabolic changes to GH occur within one week and return to control values within 8 days following withdrawal.
Technical Abstract: The purpose of these studies was to determine the time-course for changes in metabolism and physiology in response to the initiation of porcine somatotropin (pST) treatment and following withdrawal from treatment in barrows. A baseline experiment was performed using chronic pST treatment (28d, 4 mg pST/d)). pST improved feed efficiency 27%, decreased backfat thickness 43%, decreased palmitate esterification 44% and reduced glucose and lactate oxidation by 70-86% in adipose tissue. Hepatic metabolism was not affected. The next experiment examined time- course for changes in intake and metabolism in response to pST treatment (0 vs. 4 mg/d) and withdrawal in barrows over 7 days of treatment and for 8 days after withdrawal. Adipose tissue biopsies were obtained at d0, 1, 2, 4 and 7 of treatment and 2, 4, and 8 days after withdrawal. Lipogenesis was inhibited by d4 (68%); less than with chronic pST treatment. Fatty acid synthase activity declined with treatment duration, with the greatest reduction at day 7 (26%). Lipogenesis gradually increased, reaching control value 8d after withdrawal. Blood urea nitrogen concentrations decreased during pST treatment and were normalized by 4 days of withdrawal. The results indicate most of the metabolic changes in response to pST occur within one week and return to control values during withdrawal.