A simple continuous culture system for rumen microbial digestion study and effects of defaunation and dilution rates

Ground substrates and a buffer solution were continuously supplied into 500 ml culture vessels in which the contents were mixed slowly by a stirrer (6 rpm) and the excess medium removed via a small outlet chamber (overflow) by a turning wing (30 rpm). This procedure resulted in the formation of three layers in the culture vessel with different local dilution rates. The top and bottom layers, with slower dilution rates, successfully served to harbor and thus maintain the slowly growing microbes that would otherwise wash out of the system. The effects of defaunation on the microbial digestion were studied with varying nominal dilution rates of .5, 1.5, 2.5, and 4.0/d. Dry matter and cellulose digestibilities and VFA production were depressed by defaunation, and the depressions were more pronounced at higher dilution rates, suggesting a favorable effect of protozoa on rumen microbial digestion in higher producing animals.