Relative Contributions of Ruminal Bacteria, Protozoa and Fungi to Degradation of Forage Fiber Fractions

摘要

The relative capabilities of different rumen microorganisms to degrade forage fiber were compared in vitro. Forages were used, as the substrates in the culture of rumen microorganisms, were alfalfa hay and wheat straw. Microbial groups were separated by physical (sedimentation and centrifugation) and chemical (addition of various antibiotics) treatments of rumen fluid. Prepared microbial fractions were: Whole Ruminal Fluid (WRF), Bacterial (B), Protozoal (P) and Fungal (F) fractions; cocultures of B+P, B+F and P+F and a free-microorganisms rumen culture as Negative System (NS). Light microscopic observations of samples during the incubation period supported that fractionation method used for separating different microbial groups were satisfactory. The results indicated that WRF and cocultures were more effective than monocultures on dry matter loss of all forages. However, the effect of bacterial fraction on DM loss of alfalfa was equal to WRF and cocultures but more than the other two monocultures. The NDF and ADF losses of alfalfa and wheat straw were higher in the B+P than other cocultures (i.e., the P+F and B+F) and WRF. The ADL loss when averaged across both forages was highest (about 15%) due to WRF and lowest (about 8%) to protozoal fractions. In general, rumen bacterial fractions appeared to be the most active fiber degraders between rumen microorganisms. The protozoal and fungal fractions showed lower capability in this regards. However, cocultures of different rumen microbial fractions seemed to display synergetic interactions.