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Temporal changes in total and metabolically active ruminal methanogens induced by 3-nitrooxypropanol in dairy cows.

C. Pappalardo




Temporal changes in total and metabolically active ruminal methanogens induced by 3-nitrooxypropanol in dairy cows.
D. Pitta1, A. Melgar2, N. Indugu1, C. Pappalardo*1, M. Hennessy2, B. Vecchiarelli1, V. Shabtai1, M. Kindermann3, N. Walker3, A. Hristov2. 1University of Pennsylvania School of Veterinary Medicine Kennett Square, PA, 2The Pennsylvania State University University Park, PA, 3DSM Nutritional Products Basel, Switzerland.

It has been shown that enteric methane production in dairy cows peaks within 6 h post-feeding and that the mitigating effect of 3-nitrooxypropanol (3-NOP), a methane inhibitor under investigation, is highest immediately post-feeding and lowest before feeding. The effect of 3-NOP on methanogen populations in the rumen over the course of the day has not been investigated. The purpose of this study was to investigate the effect of 3-NOP on total and metabolically active methanogens in the rumen of dairy cows over the course of the day and over a 12-week period. Rumen contents of 8 ruminally-cannulated early-lactation dairy cows were sampled at 2, 6, and 10 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 microbial DNA (total) and microbial RNA (metabolically active), PCR-amplified for the 16S rDNA gene of archaea, sequenced on an Illumina platform, and analyzed for archaea diversity. There was a difference (P < 0.05) between DNA and cDNA-based archaea communities revealing that methanogens have different metabolic capacities. At the community level, weighted UniFrac analysis (commonly present populations) revealed differences (P < 0.05) by treatment, week, and their interaction. In the unweighted UniFrac analysis (presence-absence information), methanogen communities differed by treatment, week, sampling hour, and their interaction in both DNA and cDNA-based analysis. Methanobrevibacter was the dominant genus followed by Methanosphaera, with the latter genus having greater abundance in the metabolically active component compared with total populations. The relative abundance of Methanosphaera was higher at 2 h compared with 6 and 10 h after feeding, and the reverse was true for Methanobrevibacter. These findings show that Methanosphaera may increase following feed intake and may have a greater share in total methane formation than previously thought.

Keywords: enteric methane, methanogen diversity, dairy cow.