Animal Science Faculty

  Richard E. Austic  -   Professor

 

 

Email: rea2@cornell.edu

Current Research

The efficiency with which amino acids are used for growth and other physiological processes is markedly influenced in poultry and other animals by the dietary balance of amino acids and the levels of other nutrients in the diet. Relatively little is known about the molecular mechanisms by which amino acid utilization is controlled under these conditions. If mechanisms were known, it might be possible to improve the efficiency with which dietary protein and amino acids are used. Research in this laboratory focuses on nutritional interactions of amino acids in poultry and other monogastric species and the impact of interactions on requirements of amino acids for physiological processes such as growth, reproduction and immune function.

Excesses of some amino acids increase the requirements of others for growth. The effects of some excesses are mediated by suppression of food intake. However, the metabolic and physiological bases of changes in food intake are obscure. We are using two models of amino acid interactions, threonine imbalance and isoleucine imbalance (i.e., dietary excesses of other amino acids relative to threonine or isoleucine), to investigate the role of selected enzymes in amino acid imbalances. These studies focus on the mitochondrial enzymes, threonine dehydrogenase and branched-chain keto acid dehydrogenase activities which are important in the regulation of threonine and branched-chain amino acid metabolism, respectively. Studies on threonine imbalance, for example, indicate that hepatic threonine dehydrogenase activity is increased two- to three-fold in chicks and rats that are subjected to threonine imbalance. The change in rats is transitory, paralleling the adverse effects of the imbalance on growth which is also transitory in these animals. The change in threonine dehydrogenase in chicks is persistent, as is the effect of threonine imbalance on growth. We postulate that threonine dehydrogenase activity leads to altered availability of threonine in selected tissues in threonine imbalance. The regulation of threonine dehydrogenase and its role in amino acid utilization is under investigation.

Excesses of other amino acids depress growth by mechanisms that appear largely independent of food intake. The lysine-arginine interaction in which excess lysine increases the arginine requirement is one example of this kind of interaction in poultry. Excess dietary lysine increases kidney arginase activity several fold and increases the irreversible degradation of arginine to ornithine and urea. Supplementation of the diet with certain amino acids reduces renal arginase activity and the degradation of arginine and alleviates the lysine-arginine antagonism. Arginine is potentially limiting in some practical diets for poultry and is the precursor of essential metabolites that participate in a variety of physiological functions. Research in this laboratory addresses the nature of the lysine-arginine interactions at the tissue and cellular level and their impact on the arginine requirement for growth and selected physiological processes.