Gnotobiotic Ruminants in Studies into the Microbiota of the Gastrointestinal Tract

Gnotobiotic ruminants can be used to observe the development of the rumen ecosystem as well as to study the relations between rumen and its microbiota. The rumen microbiota directly affects the development of the rumen epithelium and the level of intermediary metabolism by the action of rumen fermentation and its final metabolites. Fonty and coworkers (90), using meroxenic lambs demonstrated that the functions of the rumen and the stability of the ecosystem depended on the complexity and diversity of the microbiota. In the light of the present knowledge it is not possible to precisely determine the composition of the minimum microbiota enabling rumen development and function. Fonty and coworkers (91) also studied the role of rumen microbiota in the development of the rumen ecosystem and functional development of the rumen at an early age. Their results suggest that the rumen microbiota of the very young lamb plays an essential role in the establishment of the rumen ecosystem and in the onset of the digestive functions. Those bacterial species that colonize the rumen immediately after birth when this organ is not yet active, contribute to a biotope favoring the establishment of cellulolytic strains and the set-up of digestive processes that affect both degradation of the lignocellulose-rich feeds and fermentation of the resulting soluble compounds. Ecological factors controlling the establishment of cellulotytic bacteria and ciliate protozoa in the lamb rumen were studied in meroxenic lambs (92). The results obtained in this study suggested that the establishment of cellulolytic bacteria and protozoa required an abundant and complex microbiota and was favored by an early inoculation of the animals. All above-mentioned results point at the extremely important role of the microbiota in the development of the rumen. There is a good relationship between the development of rumen function and the complexity of its microbiota. The presence of a simple microbiota cannot assure the digestive function as properly as a complex microbiota can. Bomba and coworkers (93) used the gnotobiotic approach to observe the development of rumen fermentation in lambs from birth up to 7 weeks of age in association to the complexity of the digestive tract ecosystem. The results obtained indicated that complexity of rumen microbiota significantly affected the development of rumen fermentation both from the quantitative and the qualitative viewpoint.

The fact that early inoculation of the animals is a factor favoring fermentation and digestive activities in the rumen is probably related to the action of bacteria on the development of papillae, the rumen mucosa and the digestive tract (94). A complex microbiota presents an inevitable presupposition of optimal development of the alimentary tract in ruminants.

Colonization of the individual gut segments by lactobacilli and the inhibitory effect of Lactobacillus casei upon the adhesion of enterotoxigenic E. coli K 99 to the intestinal wall were also studied in gnotobiotic lambs (74). Soares and coworkers (95) and Lysons and coworkers (96) compared several parameters of the morphological and functional development in germ-free, gnotobiotic and conventional lambs.

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