Animal & Avian Sciences Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/2741
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Item Integrating Macronutrient Metabolism In Developing Chicken Embryos(2007-12-19) Sunny, Nishanth Edakulathur; Bequette, Brian J; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The objective of this thesis research was to determine the pathways of glucose metabolism and utilization in small and large egg embryos during the latter half of development, and whether in ovo nutrient supplementation alters glucose use. A further objective was to determine the contribution of glutamate, glutamine and glycerol to glucose, glycogen and non essential amino acid (NEAA) synthesis during embryo development. In ovo stable isotope ([U-13C]glucose, [U-13C] glutamate, [U-13C]glutamine and [U-13C]glycerol) injection approaches were developed along with mass isotopomer distribution analysis of metabolic intermediates and end-products to acquire a metabolic phenotype of the fluxes and partition of these substrates through central pathways. Embryos developing in small and large eggs maintained similar rates of glucose metabolism. Thus, glucose entry and utilization gradually increased from day 12 to 18 embryonic. By embryonic day 20, gluconeogenesis accounted for >80% of glucose entry, a part (65%) of which was represented by glucose carbon recycling. Glutamate and glutamine were not found to be significant gluconeogenic precursors in day 19 embryos. However, catabolism of these amino acids contributed to ~25% of proline flux in the liver. By contrast, there was significant [M+3] 13Cisotopomer abundance in blood glucose and in liver and muscle glycogen when [U- 13C]glycerol was injected in ovo. These observations clearly confirmed that glycerol derived from triacylglycerides is a significant precursor for glucose and glycogen synthesis. In ovo supplementation on day 9 embryonic of glucose and/or amino acids (5 non-essential amino acids) did not alter gluconoegenesis. However, these supplemental treatments significantly reduced catabolism of glucose via glycolysis. 13C-Mass isotopomer abundances of most substrates differed when each was individually compared in blood and in the various tissues, indicating differences in substrate utilization between tissues. In summary, this thesis research has provided new information on the degree and pathways of nutrient (glucose, glycerol, amino acids) use by the developing embryo and the rapid adjustments in the activity of networks of enzymes involved in non-essential amino acid, glucose and glycogen metabolism to support embryo survival. Most importantly, this work has systematically evaluated the potential substrates that the embryo utilizes for glucose synthesis, in particular, the significant role of glycerol.Item Regulation of Urea Recycling into the Gastrointestinal Tract and Ammonia Metabolism in Ruminants(2004-12-08) Sunny, Nishanth Edakulathur; Bequette, Brian J; Animal Sciences; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The primary objective of this study was to determine the extent ruminants control urea recycling to the gastrointestinal tract (GIT), independent of rumen microbial metabolism. Urea kinetics were determined by continuous infusion of [15N15N]urea (4 levels) to jugular vein of sheep (n = 4; 28.1kg) fed a low protein (6.8%) diet. Although urea recycling to the GIT (P < 0.001) increased with each level of urea, the proportion (P < 0.001) and amount (P < 0.001) of recycled urea returning as ammonia to liver for ureagenesis also increased. In consequence a decreasing proportion (P = 0.003) of recycled urea was used for microbial protein synthesis. The present study suggests that ruminants have a large capacity to partition urea-N to the GIT. Thus, rather than up-regulating urea recycling, there appears to be more potential to improve N efficiency in ruminants by manipulating the rumen environment to optimize capture of recycled N.