Incorporation of radioactive carbon from [14C] alanine in the rumen of a cow given feed containing urea as the sole source of nitrogen

Abstract

The utilisation of exogenic amino acid in a cow given feed containing urea and ammonium salts as the sole sources of nitrogen was studied by means of intraruminal administration of [14C]alanine. The labelling of the trichloracetic acid-precipitated bacterial cell mass, the main volatile fatty acids (acetic, propionic and butyric acid) and a number of isolated amino acids after 1,3, 8 and 26 h was determined. The rumen micro-organisms rapidly incorporated the [14C]alanine into their cellular constituents. After the above-mentioned times the microbial cell mass was found to contain 47.4, 49.7, 70.0 and 80.0 % of the total activity of the rumen contents. Although the carbon skeleton of alanine can be used for the formation of many amino acids the rumen bacteria studied were shown to utilise only small amounts of this amino acid in their synthesis of Asp, Glu, Tyr and Phe. The combined label present in these 4 amino acids was 1.5, 1.9, 2.9 and 5.5 % of the total activity of the rumen fluid at the stated times. A considerable proportion of the [14C]alanine was degraded to volatile fatty acids: label present in acetic, propionic and butyric acid totalled 40.8, 32.3, 23.0 and 5.0 % of that in the rumen fluid. Of these, acetic acid had the strongest labelling after 1 and 3 h, and propionic acid the weakest at all stages.