Résumé:
The objective of the present work is focused on the evaluation of three Asteraceae (C. nobile, C.pulata and C. segetum) from a nutritional point of view via chemical processes (forage analysis), phytochemicals (phenolic and terpenic content) and biological (fermentability in vitro by the ruminal microbiota of cattle). The environmental aspect consisted in determining the antimethanogenic effect of these same plants as well as their respective extracts. This axis is consolidated by molecular analyzes (real-time PCR) of two microbial communities directly involved in ruminal methanogenesis (Archaea methanogens and protozoa). The practical purpose of the combination of these two approaches is shared between the formulation of dietary diets based on herbs and / or their extracts in order to provide food alternatives to local livestock, on the one hand and to control and reduce atmospheric emissions of enteric methane by ruminants, on the other hand. The chemical and phytochemical analyzes make it possible to classify C.nobile and C.pulata as substrates of good nutritional quality. This is explained by their appreciable content in total walls, their energy and protein richness and the moderate presence of antinutritional substances. Nevertheless, the high bioactive content and low protein content noted for C. segetum suggests that this plant could be valued as a natural source of bioactive substances and poorly recommended as a livestock feed. The results of the evaluation of the in vitro fermentability of the substrates studied, in terms of digestibility, in vitro gas production and fermentative profile (volatile fatty acids), are in perfect agreement with those of previous analyzes. In addition, their fermental profile indicates globally that their content of secondary substances does not influence the activity of the ruminal microbiota. Indeed, the tannoid and flavonoic fractions do not affect the different fermentation parameters after 24 hours of fermentation. The environmental aspect of the study presented by the determination of the antimethanogenic effect of plants and their extracts reveals that the fermentation of centaury increases the production of enteric methane in vitro. Noble chamomile and chrysanthemum have a tangible antimethanogenic potential with significant reduction rates (-24 and -27%, respectively). However, the antimethanogenic effect is increased (-39 and -50%, respectively) in the presence of their respective extracts. The approach of molecular biology has allowed us to have a global and rapid look at the main microbial communities directly involved in the process of ruminal methanogenesis. The results reveal the absence of a relationship between the biomass of Archaea methanogens and the production of methane in the rumen, and their existence with the protozoan community. The symbiotic relationship between these two communities could justify this finding Overall, it appears that the inclusion of C.nobile in the feeding of ruminants as basic forage is strongly recommended. C.pulata is recommended as an energy supplement, which makes it possible to propose them as good condidates for a possible exploitation in the animal feed and a probable reorganization of the courses in the steppic zones. The notable effect of the extracts studied on the reduction of methane production and especially the absence of effects on fermentative parameters (AGV and ammonia) make it possible to classify them as food additives to fight against the famous greenhouse effect.
