The fermentation of cellulose in vitro by organisms from the rumen of sheep

Abstract

Under environmental conditions similar to those in the normal rumen, cellulose, when fermented in vitro, by associative growths of microorganisms separated from actively fermenting rumen contents, yielded acetic acid, propionic acid, CO2 and methane as main products, together with smaller quantities of formic acid and butyric acid, and traces of acetaldehyde, pyruvic acid and lactic acid. Propionic acid predominated among the dissimilation products; the molecular ratio of propionic to acetic in 4 digests ranged from 1.5-1.8. The molecular ratios of CO2 to methane ranged from 3-3.8. The energy metabolism of the ruminant is discussed in light of these findings, and it is concluded that the useful energy of the dissimilation products would be between 85 and 88% of the combustible energy of the cellulose (i.e., between 3.6 and 3.7 kg.cal./g. cellulose) if the acetic acid enters without loss into productive channels of metabolism, and between 67 and 72% of the combustible energy of the cellulose (i.e., between 2.8 and 3 kg.cal./g. cellulose) if the acetic acid is oxidized and wastefully dissipated.