Location: Cool and Cold Water Aquaculture ResearchTitle: Effect of dietary lysine on hepatic lysine catabolism in broilers Author
Submitted to: Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/8/2013
Publication Date: 9/20/2013
Publication URL: http://handle.nal.usda.gov/10113/57950
Citation: Kiess, A.S., Manangi, M.K., Cleveland, B.M., Wilson, M.E., Blemings, K.P. 2013. Effect of dietary lysine on hepatic lysine catabolism in broilers. Poultry Science. 92: 2705-2712. dx.doi.org/ 10.3382/ps.2012-02805. Interpretive Summary: In all animals lysine is an amino acid that is essential for optimal growth rates. Determining how different levels of dietary lysine affect growth and lysine metabolism is critical for optimizing the use of dietary lysine. Both a lysine-deficient and a lysine-excess diet reduce weight gain in young chickens. A lysine-deficient diet also affects the metabolic processes that degrade lysine, suggesting that dietary lysine is itself a regulator of its own metabolism. Interestingly, the modes of regulation in chickens are different than what has been observed in rainbow trout, suggesting that mechanisms regulating lysine metabolism differ between species. These observations contribute to the development of new diets or husbandry practices that reduce feed costs, improve growth performance, and reduce nitrogen/phosphorus output of swine, poultry, and aquaculture operations.
Technical Abstract: Lysine is frequently a first- or second-limiting amino acid in poultry diets. Improving the efficiency of lysine use for protein synthesis would effectively lower the lysine requirement and decrease feed costs. Understanding how lysine is degraded and how the degradation is regulated would identify potential molecular targets for interventions to decrease lysine degradation. To better understand lysine degradation in poultry, three studies using chicks fed different levels of lysine were conducted. Measures of liver lysine catabolism including lysine alpha-ketoglutarate reductase (LKR) and lysine oxidation (LOX) were assessed. The a-aminoadipate d-semialdehyde synthase (AASS) is a bifunctional enzyme composed of both LKR and saccharopine dehydrogenase activities and the relative abundance of this protein and mRNA were likewise assessed. Moreover, potential alternative pathways of lysine catabolism that depend on L-amino acid oxidase (AAOX) and on lysyl oxidase (LYLOX) were considered. In study one, chicks, 14 days of age, fed lysine-deficient diets had decreased (P<0.05) LKR activities compared to chicks fed at or above the requirement. However, the lowered LKR activities were not associated with a decreased (P>0.05) LOX as measured in vitro. In studies two and three, chicks 28 days of age did not decrease LKR activity (P>0.05) in response to a lysine-deficient diet. No changes in AASS protein abundance or mRNA were detected. Likewise, no differences in the mRNA abundances of neither AAOX nor LYLOX were detected. The activity of AAOX did increase (P<0.05) in birds fed a lysine-adequate diets compared to those fed a lysine-deficient diet. Based on kinetic parameters and assumed concentrations, AAOX could account for about 20% of liver lysine oxidation in the avian.