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Nutritionnal regulation of hepatic metabolism of amino acids in growing ruminant: consequences on supply of nitrogenous nutrients to the muscle.

Guillaume Kraft
Abstract : The management of production efficiency is an important issue in meat producing ruminants. An improvement of the feeding allowances (including the ratio between nitrogen and energy supply) could increase the efficiency of nitrogen utilisation by animals. The splanchnic bed (portal drained viscera + liver) is in competition with the muscle for nitrogen utilisation because it represents only 6 % of body protein but contributes to 35% of whole body protein synthesis. The first aim of this thesis was to know the consequence of an imbalanced nitrogen (N) or energy (E) supply compared with a diet offering balanced supply necessary for growth (T) on the efficiency of amino acid (AA) utilisation by the splanchnic bed and the whole body of growing lambs. No (or small) alteration of nitrogen retention or growth was observed for the N fed animals compared with T, which led to an increased efficiency of nitrogen utilisation. On the contrary, lower nitrogen retention and growth were observed in E fed lambs. The second aim of this work was to determine which metabolic pathways were involved in the alterations of net hepatic AA removal. Labelled AA infusion in catheterised animals allowed the measurement of net fluxes of nutrients and irreversible loss rates of the labelled AA across the splanchnic bed (and hepatic export protein synthesis). In N fed lambs, the lower hepatic removal of AA was connected with a probable decreased hepatic catabolism of AA (except for branched chain AA) associated with a maintained protein synthesis, allowing an overall sparing of AA. On the opposite, in E fed lambs, an increased gluconeogenesis from AA and hepatic catabolism of AA (increased ureagenesis) could explain the lower nitrogen retention observed. The last aim of this thesis was to highlight some regulatory factors that could explain the metabolic adaptations observed in the splanchnic area. An ex vivo study using liver slices taken from lambs fed the 3 experimental diets, showed a higher efficiency for AA utilisation in all metabolic pathways using AA in N fed lambs. This might be related to a higher AA transport activity. On the other hand, with E diet, no significant difference was observed for protein synthesis, gluconeogenesis and oxidation compared with T, which means that external regulatory mechanisms (such as nutrients, hormones (insulin, glucagon)) are probably involved in the decrased hepatic protein synthesis observed in vivo. Thus, the nitrogen allowances should be re-evaluated for growing ruminants since our results suggest that INRA allowances overestimate the nitrogen requirements for lambs. On the opposite, energy allowances seem to fit well with the requirements and should not be reduced in order to maintain protein retention in animals.
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Theses
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https://pastel.archives-ouvertes.fr/pastel-00004957
Contributor : Ecole Agroparistech <>
Submitted on : Thursday, April 23, 2009 - 8:00:00 AM
Last modification on : Tuesday, October 20, 2020 - 10:22:16 AM
Long-term archiving on: : Friday, September 10, 2010 - 1:12:58 PM

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  • HAL Id : pastel-00004957, version 1

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Guillaume Kraft. Nutritionnal regulation of hepatic metabolism of amino acids in growing ruminant: consequences on supply of nitrogenous nutrients to the muscle.. Life Sciences [q-bio]. AgroParisTech, 2009. English. ⟨NNT : 2009AGPT0001⟩. ⟨pastel-00004957⟩

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