Effect of fibre- and starch-rich finishing diets on methanogenic Archaea diversity and activity in the rumen of feedlot bulls

International audienceMethanogenesis plays an important role in maintaining low hydrogen partial pressure in the rumen and consequently in feed digestion. Diet composition and lipid supplementation are known to influence the extent of methane (CH(4)) production in ruminants. However, the impact of diet composition on rumen methanogens is poorly understood. This study examined CH(4) production and methanogen community abundance, diversity and metabolic activity in the rumen of fattening bulls fed a fibrous diet (F; n = 10) or a starch rich diet supplemented with extruded linseed (SL; n = 10). Net CH(4) emissions from bulls fed SL were lower than emissions from bulls fed F. Methanogenic Archaea were studied using culture independent methods targeting the functional mcrA gene. Methanogen abundance was similar in the two groups of bulls, but protozoa numbers were 65% lower in the F group. The SL diet decreased methanogen diversity and metabolic activity, which were evaluated by PCR-DGGE and reverse transcriptase qPCR, respectively. In contrast, no changes occurred in bacterial numbers and diversity between diets. Data indicate that reduction in net CH(4) production with the SL diet was associated with changes in rumen microbiota, particularly methanogen activity. Characterization of the activity and structure of the whole rumen microbiota should provide a better prediction of methanogenesis