Use of ratio of digested xylan to digested cellulose (X/C) as an index of fiber digestion in plant cell-wall material by ruminal microorganisms

Traits in digestion of plant cell-wall components of timothy (Phleum pratense) hay were studied in pure cultures of ruminal fibrolytic microorganisms and in sacco. Four strains of rumen bacteria, Butyrivibrio fibrisolvens D1 (ATCC19171), Fibrobacter succinogenes S85 (ATCC19169), Prevotella ruminicola subsp. brevis 7-31, and Ruminococcus albus 7, and four strains of anaerobic fungi, Neocallimastix frontalis MCH3, Piromyces communis 93-3, Piromyces sp. P1 and polycentric fungus KP1, were used in this experiment. Each microorganism was inoculated on ground timothy hay (20 g l−1) in an anaerobic medium and incubated at 39°C. Dry matter loss of timothy hay and digested xylan to digested cellulose (X/C) ration of the substrate during incubation were determined. The X/C ratios in the cultures of Pre. ruminicola and B. fibrisolvens were greater than 0.5. Those of R. albus, Pir. communis, Piromyces sp. P1 and N. frontalis were between 0.3 and 0.5. Those of F. succinogenes and polycentric fungus KP1 were lower than 0.3. The X/C ratios observed in sacco were around 0.2 and close to those of F. succinogenes. The similarity of the digested X/C ratios between F. succinogenes and in sacco measurements suggests that F. succinogenes plays a predominant role in fiber digestion in the rumen.