Development of methods to improve the estimation of threonine catabolism in the growing pig

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Simpson, Gregory James

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University of Guelph

Abstract

Current estimates of threonine catabolism in growing pigs are variable. Threonine catabolism is initiated by two main pathways: threonine-3-dehydrogenase (TDG, EC 1.1.1.103) and threonine dehydratase (TDH, EC 4.2.1.16). The application of multiple isotope tracers to directly estimate threonine catabolism requires the development of a threonine-limiting diet and the identification of major site(s) of threonine catabolism. A synthetic casein-and-cornstarch-based threonine-limiting diet was formulated using literature values for aspects of threonine utilization to estimate threonine requirements for body protein deposition. The nitrogen balance method confirmed this diet was threonine-limiting. Enzyme assays for TDG and TDH were used to identify major sites of threonine catabolism in the pig. The main sites of TDG activity were the liver and pancreas. TDH activity was similar in liver, heart, kidney, duodenum, pancreas and muscle tissues. These findings can be applied to the improvement of a multiple tracer approach to estimate threonine catabolism in growing pigs.

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growing pigs, threonine catabolism, threonine-limiting diet, liver, pancreas

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