Browsing by Author "Escobar, Jeffery E."

Now showing 1 - 3 of 3
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    Impact of exogenous factors on amino acid digestibility in non-ruminants
    Lee, Hanbae (Virginia Tech, 2012-04-30)
    The nutritional value of an amino acid (AA) is determined by its bioavailability, however concept of digestibility is mostly used in practical situations. Four studies were conducted to test 2 exogenous factors that were hypothesized to affect the AA digestibility in non-ruminant animals. In study 1, broiler chicks were randomly allotted to 4 dietary treatments of control and distillers dried grains with solubles (DDGS, 20%) diets supplemented or not with a novel mixture of carbohydrases. Results indicated the ability of carbohydrase mixture to increase energy utilization of the DDGS diet, with significant improvements in AA digestibility, consequently improving growth performance of broilers. Study 2 examined effect of the carbohydrase mixture in pigs fed a high DDGS diet. Ileal cannulated growing pigs (n = 8, 64.3 ± 0.5 kg) were allotted to 4 dietary treatments in a replicated 4 Ã 4 Latin Square design. Control and DDGS (40%) diets were supplemented or not with a mixture of carbohydrases. Numeric increases for AA digestibility, along with a decreased tendency of urinary energy output suggested a possibility for improved nutrient utilization in pigs when carbohydrases were supplemented to 40% corn DDGS diet. Collectively, carbohydrase seems less effective for swine applications due to greater water content and consequently a lower viscosity in pig digesta. Next, study 3 showed changes in AA digestibility and endogenous AA losses (EAAL) when pigs were challenged orally with Salmonella enterica serovar Typhimurium. Nursery pigs (n = 48, 17.9 ± 0.5 kg) were randomly assigned to a 2 Ã 2 factorial arrangement consisting of two diets (control or N-free) and inoculation (sterile broth or 9.8 Ã 10^9 CFU of Salmonella). Measurements at 24 and 72 h post-inoculation indicated that AA digestibility of pigs is impaired through the initial phase of Salmonella infection and gradually restored, but not fully by 72 h. Finally, study 4 determined the dynamic fluctuations of EAAL and subsequent AA digestibility in response to Salmonella Typhimurium measured at multiple time points. Ileal cannulated pigs (n = 8, 76.0 ± 1.4 kg) were randomly assigned to either a control or a N-free diet and challenged orally with 1.3 Ã 10^10 CFU of Salmonella. Inflammatory diarrhea was associated with reduced AA digestibility and increased EAAL showing respective peak values at 8-16 h post-inoculation. Alterations in AA digestibility and EAAL were gradually recovered to near pre-inoculation values by 56-64 h post-inoculation, but showed impaired digestibility at 72-80 h post-inoculation.
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    Plasma amino acid and metabolite changes in pigs during endotoxemia
    Price, Kathryn Leigh (Virginia Tech, 2011-11-15)
    The nutritional status, especially circulating amino acid (AA) levels, can drastically change during a non-infectious (i.e., LPS) or infectious (e.g., Salmonella) challenge. Thus, study 1 examined the effect of LPS treatment (N = 9, 26.9 ± 1.07 kg BW) on plasma AA and metabolite levels in pigs. Data were used to generate prediction equations establishing mathematical relationships between plasma AA levels and numerous blood metabolites (e.g., total lipid, LDL, HDL, blood urea nitrogen, etc). These equations have the potential to improve the nutritional treatment and recovery of acute and chronically ill patients. Study 2 (19.1 ± 0.37 kg) was a continuation of study 1 except the sampling time was increased from 12 to 24 h. One-half of the pigs in study 2 were treated with LPS (N=15) and the other one-half were saline treated control animals (N = 16). This design allows for monitoring changes in plasma AA and their catabolism in response to endotoxemia. Area under the curve (AUC) was calculated for a selected AA to report AA balances. During the induction phase of an acute challenge (t = -2 to 12 h), analyzed AA were in a negative balance indicating heavy AA catabolism. However, during the recovery phase (t = 12 to 24 h) half of the AA were in a positive balance while the other half were still negative. The ability of equations to accurately predict AA concentrations was tested. Results indicate poor performance possibly due to heavy term biases. Thus, it was concluded that equations need to be revisited and non-linear terms need to be evaluated. Nonetheless, routine clinical blood metabolites can be used to estimate plasma AA levels during immune activation. We successfully established a porcine Salmonella enterica serovar Typhimurium model. Pigs infected with Salmonella had a febrile response for 4 d and exhibited marked changes in their fecal bacterial populations Finally, we investigated plasma changes in N-τ-methyl histidine (NτMH) in healthy and LPS-treated pigs. NτMH— is a post-translationally modified AA that has historically been used as an indirect marker of muscle protein breakdown in rodents and humans. However, the major form (i.e., free or acetylated) of NτMH in pig plasma was unknown. Results indicate that only 15% of plasma NτMH is in the free form and the remainder is acetylated. Furthermore, LPS treated pigs had increased acetylated and total NτMH fractions while free NτMH did not change. Therefore, to accurately monitor plasma changes in NτMH as an indicator of muscle proteolysis, plasma samples must be subjected to acid hydrolysis.
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    Roles of Growth Hormone, Insulin-Like Growth Factor I, and Sh3 and Cysteine Rich Domain 3 in Skeletal Muscle Growth
    Ge, Xiaomei (Virginia Tech, 2012-01-12)
    Three studies were conducted to achieve the following respective objectives: 1) to determine the cellular mechanism by which growth hormone (GH) stimulates skeletal muscle growth; 2) to identify the signaling pathways that mediate the different effects of insulin-like growth factor I (IGF-I) on skeletal muscle growth; and 3) to determine the role of a functionally unknown gene named SH3 and cysteine rich domain 3 (STAC3) in myogenesis. In the first study, the myogenic precursor cells, satellite cells, were isolated from cattle and allowed to proliferate as myoblasts or induced to fuse into myotubes in culture. GH increased protein synthesis without affecting protein degradation in myotubes; GH had no effect on proliferation of myoblasts; GH had no effect on IGF-I mRNA expression in either myoblasts or myotubes. These data suggest that GH stimulates skeletal muscle growth in cattle in part through stimulation of protein synthesis and that this stimulation is not mediated through increased IGF-I mRNA expression in the muscle. In the second study, the signaling pathways mediating the effects of IGF-I on proliferation of bovine myoblasts and protein synthesis and degradation in bovine myotubes were identified by adding to the culture medium rapamycin, LY294002, and PD98059, which are specific inhibitors of the signaling molecules mTOR, AKT, and ERK, respectively. The effectiveness of these inhibitors was confirmed by Western blotting. Proliferation of bovine myoblasts was stimulated by IGF-I, and this stimulation was partially blocked by PD98059 and completely blocked by rapamycin or LY294002. Protein degradation in myotubes was inhibited by IGF-I and this inhibition was completely relieved by LY294002, but not by rapamycin or PD98059. Protein synthesis in myotubes was increased by IGF-I, and this increase was completely blocked by rapamycin, LY294002, or PD98059. These data demonstrate that IGF-I stimulates proliferation of bovine myoblasts and protein synthesis in bovine myotubes through both the PI3K/AKT and the MAPK signaling pathways and that IGF-I inhibits protein degradation in bovine myotubes through the PI3K/AKT pathway only. In the third study, the potential roles of STAC3 in myoblast proliferation, differentiation, and fusion were investigated. Overexpression of STAC3 inhibited differentiation of C2C12 cells (a murine myoblast cell line) and fusion of these cells into myotubes, whereas knockdown of STAC3 had the opposite effects. Either STAC3 overexpression or STAC3 knockdown had no effect on proliferation of C2C12 cells. Myoblasts from STAC3-deficient mouse embryos had a greater ability to fuse into myotubes than control myoblasts; the former cells also expressed more mRNAs for the myogenic regulators MyoD and myogenin and the adult myosin heavy chain protein MyHC1 than the latter. These results suggest that STAC3 inhibits myoblast differentiation and fusion.