Conversion of C-labeled substrates to volatile Fatty acids by the rumen microbiota.

The fermentation of uniformly labeled glucose-C, glucose-1-C, -2-C, and -6-C, xylose-1-C, cellulose-1-C, -2-C, and -6-C, and lactate-2-C by rumen fluids from cows fed all-hay, hay and concentrate (50:50), and all-concentrate diets was investigated. The results obtained suggested that the Embden-Meyerhof glycolytic pathway is the major pathway of hexose utilization, that the major pathway of xylose fermentation involves hexose synthesis, and that the contributions of the nonrandomizing (acrylate) pathway of propionate formation during glucose, xylose, and cellulose fermentations are 4.5, 8.0, and 10.5%, and 24.6, 25.8, and 17.2%, respectively, by rumen fluids from the cows fed all-hay and all-concentrate rations.