Most-probable-number procedures for enumerating ruminal bacteria, including the simultaneous estimation of total and cellulolytic numbers in one medium.

Based on results from eight experiments, no overall difference was found between roll tube and three- and five-tube most-probable-number (MPN) methods for estimating total numbers of ruminal bacteria. However, standard errors for the replicate means within an experiment were higher with the MPN procedures. Visual growth and pH were the criteria used for scoring the MPN tubes. Total numbers were significantly higher in MPN medium containing 40% ruminal fluid, as compared with a complete medium without ruminal fluid. By using a broth medium containing ball-milled cellulose and soluble carbohydrates as energy sources, it was possible to estimate both total and cellulolytic ruminal bacterial numbers in the same MPN series. Disappearance of cellulose and decrease in pH were used to determine growth. Values did not differ from those obtained in separate MPN assays. By using this method, diurnal changes in total and cellulolytic bacterial numbers were estimated in sheep fed forage or a concentrate-type diet.