Relationship between bacteria and ciliate protozoa in the rumen of sheep fed on a purified diet

Abstract

Two sheep, with and without ciliate protozoa, were fed on a wood-pulp cellulose, corn starch, soya-bean protein diet and the microbiological and chemical characteristics of the rumen ingesta of both sheep were studied. The purified diet led to a simplified rumen flora enabling some deductions to be made about the interactions of the principal bacterial species and their interactions with the protozoa in relationship to the biochemical analysis of the rumen. Ammonia concentrations were similarly low in each animal. Total volatile fatty acid concentrations were higher in the faunated sheep though the proportion of propionic acid was highest in the unfaunated sheep. Cellulose digestion in the faunated rumen was about twice that in the unfaunated one. Total bacterial concentrations in the unfaunated rumen were over twice those in the faunated rumen, but the numbers of cellulolytic bacteria were higher in the latter while the numbers of amylolytic bacteria were higher in the unfaunated rumen. The principal species of bacteria differed in the two rumens. INTRODUCTIONThe natural rumen flora contains both bacteria and ciliate protozoa, but the role of the protozoa in rumen function and the relationships between the protozoa and bacteria are not completely understood. Animals can be, by partial isolation, reared without rumen ciliate protozoa, or the organisms can be removed from the rumen population by chemical additives or by change in feed to one producing rather acidic rumen conditions (Eadie, 1962;Abou Akkada et al. 1968;Eadie et al. 1970). Investigations of metabolic activities of the protozoa have shown that they are essentially similar to those of the bacteria so far as the main functions of the rumen are concerned, that is they use carbohydrates as energy sources and form acidic fermentation products and cell material which are utilized by the host animal. Because of this, the fact that on most diets the protozoa perform only a minor part of the total rumen metabolism, and in many cases rumen bacterial concentrations have been found to be higher in unfaunated than faunated animals, unfaunated animals are not

Effects of defaunation on microbial activities in the rumen of rams consuming a mixed diet (fresh Digitaria decumbens grass and concentrate)

“…Our results on the effect of defaunation on some enzymatic microbial activities confirm previous studies [15,21]. Despite a high variability of the values, the determination of the evolution of a microbial population after defaunation, with modern tools can give good results.…”

“…Defaunation decreased the total activity of the fibrolytic enzymes of the solid adherent microorganisms. Similar results were obtained by Kurihara et al [21]. This decrease could be attributed to the decrease of the specific activity of these enzymes and/or to the decrease of the number of fibrolytic microorganisms that produce these enzymes.…”

“…The decreased molar proportion of butyrate observed after defaunation is coherent with the elimination of protozoa after defaunation, which are important butyrate producers [4,14]. Moreover, amylolytic bacteria, which produced succinate which is then decarboxylated by Selenomonas ruminantium to give propionate, are reported to increase after defaunation [7,21]. Indeed, protozoa ingest a high number of starch grains and amylolytic bacteria are associated with them [15].…”

Influence of the presence of protozoa on the rumen microbial population of cattle.

“…constituted approximately 47% of bacterial population in the rumen of two animals during unfaunated period, but this percentage decreased by approximately 20% after the inoculation of protozoa. These results agree with those of Bryant and Small (4), and of Kurihara et al (16). The rumen bacterial population of two animals after the inoculation of protozoa was dominated by Butyrivibrio spp., Bacteroides spp., Selenomonas spp., and Clostridium spp.…”

Influence of substrate and microbial interaction on efficiency of rumen microbial growth

“…total synthesis-degradation). The efficiency of net microbial N incorporation (E) was increased by defaunation, not only because of elimination of turnover due to protozoal lysis and predation, but also because of a shift to a faster-growing amylolytic flora (Kurihara et al, 1978), as indicated by the increased efficiency of total synthesis. These results obtained in vitro have recently been confirmed in a number of animal experiments and it is clear that variability in microbial N yields may be determined to a large extent by variability in the number and activity of rumen protozoa, quite apart from energy yield in fermentation (Demeyer and Vervaeke, 1984).…”