Effect of Dietary Protein Levels, Amino Acid Supplementation and Nitrogen Source upon the Plasma Free Amino Acid Concentrations in Growing Lambs

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Abstract
A study involving a growth trial and the examination of plasma free amino acids was carried out using 24 lambs in a 4 × 2 factorialized experiment in which 4 dietary protein levels and the presence or absence of L-lysine and DL-methionine in the diets were treatments. Although only plasma methionine, which decreased with increased dietary protein levels and also with dietary amino acid supplementation, was statistically significantly affected by the treatments, upward trends in most of the plasma amino acid concentrations with increasing dietary protein levels were apparent. Other exceptions to the general trend were lysine and histidine plasma concentrations which did not change appreciably. Supplementation of the diets with 0.24% lysine and 0.19% methionine did not increase the plasma concentrations of lysine or methionine. In a second experiment involving 9 lambs fed a purified diet in which urea was the sole source of nitrogen the plasma amino acid concentrations were considerably lower for most of the amino acids. Exceptions were glycine and serine which were higher in plasma of lambs fed the purified diet. In a third experiment the rumen contents from lambs fed a purified diet with urea as the sole nitrogen source were hydrolyzed and the amino acid content was determined. The amino acid content and amino acid ratio of rumen contents are compared with that of whole egg protein.