Résumé:
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.
