Impact de plantes riches en métabolites secondaires sur la méthanogénèse ruminale et les activités fermentaires du microbiome ruminal chez des ovins

Abstract

Strategies of methane reduction will have to take into account the other environmental impacts and the social-economic stakes. Therefore, the main encouraging way envisaged to reduce enteric methane is the use of additives containing plants secondary metabolites. The objective of this thesis work was to test at first the in vitro potential of essential oil extracts and condensed tannins-rich plants to reduce methane production. Secondly, an in vivo study was conducted for a validation of results obtained in vitro and for a better knowledge of ruminal methanogenesis and fermentative phenomena. Our work allows concluding that essential oil and condensed tannins have the potential to decrease in vitro methane production. Essential oils of Mentha pulegium and Juniperus phoenicea negatively affect in vitro ruminal fermentation. Condensed tannins reduce in vivo methane production without notable unwanted effects on ruminal fermentation and on digestibility. The effect of condensed tannins is rather linked to the dose and not to the nature of the plant. This work also highlighted the absence of relation between concentration and diversity of methanogens and methanogenesis. Reduction of methane is due to the inhibition of the activity of methanogens rather than to the decrease of their concentration. The presentation of tannins rich plants under granular shape had also accelerated the transit. Results from the in vivo study suggests that dietary condensed tannins from Leucaena leucocephala, Manihot esculenta, and to a lesser extent from Gliricidia sepium in pellet form could be used to mitigate methane production with no marked detrimental effects on other fermentative parameters.