The present report describes an in vitro continuous culture system to simulate rumen fermentation. The complete assembly consists of six culture vessels (liquid volume 700 ml) fed twice daily with finely ground feed. The artificial saliva enters the vessel continuously, and the effluent leaves it continuously through the overflow port. The intermittent stirring of the fermentor content and the pH regulation are automatically controlled by a desktop computer. Two replicate experiments with ten fermentors given a diet of silage (50 %) and barley (50 %) were made in order to evaluate the system. The results indicate that the system reaches steady-state conditions within three to five days, ammonia concentration being an exeption. It takes for the ammonia concentration approximately 11—14 days to stabilize. The plateau values for the total volatile fatty acid (VFA) concentrations, the molar proportions of individual VFAs, and the ammonia concentrations were found to be within the accepted range in the rumen of animals given similar diets or in other artificial rumen systems. There was a tenfold decrease in the numbers of protozoa in the fermentors during the first four days of incubation. However, the average plateau value for the protozoa numbers (2.5 x 104/ml) is in the same range as in the dual flow continuous culture systems. The efficiency of the microbial N production was higher than that usually observed in vivo or in vitro (45 vs. 30 g/kg organic matter digested). The results indicate that this continuous culture system provides a reasonable estimate of rumen fermentation.
Nitrogen isotope fractionation in a continuous culture system containing phytoplankton and blue mussels
