Relationship Between Ornithine and Proline in Chick Nutrition

Studies were performed to investigate the metabolic relationship between ornithine and proline, and the ability of chicks to use ornithine as a proline source. Day-old chicks (N.H.×S.C.W.L. cross or broiler-type chicks) were fed a synthetic L-amino acid diet with and without proline or ornithine·HCl for two weeks. The result s indicated that the inclusion of L-proline (0.68% or 1.0%) in the diet fed caused a marked increase in growth rate, feed efficiency and plasma proline level when compared with those chicks fed a diet without proline. The addition of ornithine·HCl at 2% but not 1% to the diet also caused some improvements in growth but not as good as those fed diets containing proline. Feed efficiency was not improved by additional ornithine·HCl both at 1% and 2%. The plasma proline level was increased with the increases in dietary ornithine·HCl levels. In in vitro studies, livers from chicks (ages 17 to 21 days) were homogenized. The liver homogenate was then incubated in a potassium phosphate buffer system (pH 7.4) containing various substrates for 30 minutes. The formation of Δ1-pyrroline-5-carboxylic acid and of proline in the reaction mixture were determined. The data showed that ornithine could be converted to Δ1-pyrroline-5-carboxylic acid and proline. Exogenous α-ketoglutaric acid was required for the optimal conversion of ornithine to both Δ1-pyrroline-5-carboxylic acid and proline. Arginine was utilized for the in vitro synthesis of Δ1-pyrroline-5-carboxylic acid to a very limited extent, and was not immediately utilized for the formation of proline.