Criteria for Establishing the Validity of in vitro Studies with Rumen Micro-organisms in so-called Artificial Rumen Systems

Abstract

SUMMARY: Several criteria of normal rumen function which can be applied to in vitro studies with the whole rumen microbial population are suggested. These include: the maintenance of numbers and normal appearance of the bacteria, selenomonads and protozoa of the rumen; the maintenance of normal rates of digestion of cellulose, starch and protein, and of normal interactions between these; the ability to predict quantitative results in vivo. An ‘artificial rumen’ was constructed, consisting of a cellophan sac containing rumen liquor and substrate dialysing against a complex mineral solution whose composition was based on that found in rumen liquor, the whole being incubated at 39° in an atmosphere of nitrogen and carbon dioxide. This system was shown to meet the criteria which are suggested, with reasonable success for periods of about 8 hr.; over longer periods an increasing failure to meet the biological criteria was seen. For the microbial population to remain normal in numbers and activity it was shown to be necessary to use as test substrate in vitro only substances similar to the diet fed to the animal from which the rumen liquor inoculum was taken.