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The effect of 3-nitrooxypropanol on ruminal microbial gene expression in dairy cows.

D. Pitta




The effect of 3-nitrooxypropanol on ruminal microbial gene expression in dairy cows.
D. Pitta*1, A. Melgar2, N. Indugu1, V. Shabtai1, M. Hennessy1, B. Vecchiarelli1, M. Kindermann3, N. Walker3, R. Thauer4, A. Hristov3. 1University of Pennsylvania School of Veterinary Medicine Kennett Square, PA, 2The Pennsylvania State University University Park, PA, 3DSM Nutritional Products Basel, Switzerland, 4Max Planck Institute for Terrestrial Microbiology Marburg, Germany.

Research indicates that 3-nitrooxypropanol (3-NOP), a methane inhibitor under investigation, reduces enteric methane emissions by an average of about 24% in dairy cows. However, studies on the contribution of different methanogens to methanogenesis in the rumen and the effect on these pathways by 3-NOP are lacking. The purpose of this experiment was to investigate the effect of 3-NOP on inhibition of different methanogenesis pathways in dairy cows fed silage-based diets over a 12-week period using metatranscriptomics. Rumen contents of 8 ruminally-cannulated early-lactation dairy cows were sampled 2 h after feeding during wk 4, 8, and 12 of a randomized complete block design experiment in which 3-NOP was fed at 60 mg/kg feed dry matter intake. Cows (4 control and 4 3-NOP) were blocked based on their previous lactation milk yield or predicted milk yield. Rumen samples were extracted for RNA and reverse transcribed to cDNA. Libraries were then constructed, sequenced on the Illumina HiSeq platform, and sequences were annotated against the KEGG database. Three methanogenesis pathways were identified: the hydrogenotrophic (CO2 + H2) pathway was the predominant pathway (contributing to about 70% of methanogenesis in the rumen in this experiment), followed by the methanol-utilizing (15%) and methylamine-utilizing pathways (10%). Six species of Methanobrevibacter, 2 species of Methanosphaera, and Methanomassiliicoccales representatives were involved in the hydrogenotrophic pathway, methanol-reducing, and methylamine-reducing methanogenesis pathways, respectively. The most abundant archaeal transcripts were those of genes encoding the α, β, and gamma chains of methyl co-enzyme reductase (MCR), an enzyme that facilitates the formation of methane and is present in all methanogens. This study showed that 3-NOP numerically reduced MCR transcripts by 4, 30, and 12% at wk 4, 8, and 12, respectively, accompanied by a 25% reduction in enteric methane (g/kg ECM, P < 0.0001). It can be concluded that inhibition of the MCR enzyme in ruminal methanogens is responsible for the reported reduction in enteric methane emission by 3-NOP.

Keywords: enteric methane, rumen microbe, dairy cow.