The contributions of bacteria and protozoa to ruminal forage fermentation in vitro, as determined by microbial gas production

Fermentation of hay and barley straw by rumen bacteria and protozoa has been compared using gas production as a measure of fermentative activity. Increasing bacterial density resulted in an increased rate of fermentation, up to a maximum rate after which the addition of further bacteria was ineffective. The addition of protozoa to a suspension of bacteria which was at the optimum concentration for fermentation did not further increase fermentation. Thus it appears that rumen protozoa do not exert a stimulatory effect on the bacterial population within the rumen. Although both the bacterial and protozoal populations are highly cellulolytic, if all available degradative niches are filled by either the bacteria or the protozoa, then the addition of the complementary population does not increase either the rate or, the extent of fermentation of the forages tested.