The synergistic and inhibitory interactions observed between Fibrobacter succinogenes A3c, Prevotella ruminicola H2b, and Ruminococcus flavefaciens B34b in the digestion of forage cellulose were studied in detail. Orchardgrass and alfalfa hays, both at two maturity stages, were used as substrates. Sequential inoculation procedures were developed whereby a second inoculation was made after the initial fermentation was killed. Total cellulose digestion from sequential addition of the organisms was then compared to values obtained in simultaneous co-culture. When the noncellulolytic P. ruminicola was co-cultured with either of the two cellulolytic species (F. succinogenes or R. flavefaciens) forage cellulose digestion numerically increased over that of the cellulolytic species alone. In contrast, decreases from co-culture values were noted with sequential addition of the organisms. When F. succinogenes and R. flavefaciens were co-cultured, cellulose digestion was reduced compared to F. succinogenes alone. However, no such reduction was observed when the organisms were added sequentially. Further experiments indicated that this inhibitory activity is only produced when the organisms are co-cultured and is stable to autoclaving at 121 degrees C for 20 min. Inhibition of this type could be the result of bacterocin production by one of the organisms; however, most bacterocins are destroyed by autoclaving. Copyright © . .

The diversity of bacteria present in the caecum of the rabbit was investigated. Partial bacterial 16S rRNA genes from a digested sample collected from the caecum of an adult rabbit were amplified by PCR. Sequence analysis of the amplified fragments indicated highest similarity was to bacterial sequences previously described from other gut environments. However, only one sequence showed significant identity (97% threshold) to any previously described bacterial 16S rRNA genes. Furthermore, most of the sequences clustered together in groups lacking representatives from sequences already described, suggesting that the rabbit caecal flora contains organisms not previously described.

In vitro rumen fermentation systems are often adapted to forage feeding conditions, with pH values ranging in a range close to neutrality (between 6.5 and 7.0). Several attempts using different buffers have been made to control incubation pH in order to evaluate microbial fermentation under conditions simulating high concentrate feeding, but results have not been completely successful because of rapid exhaustion of buffering capacity. Recently, a modification of bicarbonate ion concentration in the buffer of incubation solution has been proposed, which, together with using rumen inoculum from donor ruminants given high-concentrate diets, allows for mimicking such conditions in vitro. It is important to consider that the gas volume recorded is in part directly produced from microbial fermentation of substrates, but also indirectly from the buffering capacity of the medium. Thus, the contribution of each (direct and indirect) gas source to the overall production should be estimated. Another major factor affecting fermentation is the rate of passage, but closed batch systems cannot be adapted to its consideration. Therefore, a simple semicontinuous incubation system has been developed, which studies the rate and extent of fermentation by gas production at the time it allows for controlling medium pH and rate of passage by manual replacement of incubation medium by fresh saliva without including rumen inoculum. The application of this system to studies using high concentrate feeding conditions will also be reviewed here.