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Effect of 3-nitrooxypropanol on total and metabolically active bacteria and archaea interactions in the rumen of dairy cows.

N. Indugu



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Effect of 3-nitrooxypropanol on total and metabolically active bacteria and archaea interactions in the rumen of dairy cows.
D. Pitta1, A. Melgar2, N. Indugu*1, V. Shabtai1, M. Hennessy1, B. Vecchiarelli1, 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.

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, the effect of 3-NOP on rumen microbes is unknown. The purpose of this study was to investigate the effect of 3-NOP on total and metabolically active ruminal bacteria and archaea in dairy cows over a 12-week period. Whole ruminal 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. The solid ruminal fraction was extracted for DNA and RNA, PCR-amplified for the 16S rDNA gene of archaea and bacteria, sequenced and analyzed for bacteria and archaea diversity. Concentration of dissolved hydrogen (H2) increased at wk 4 and 8 and then decreased in 3-NOP supplemented cows compared with control cows. There was a difference (P < 0.05) between DNA and cDNA-based bacteria and archaea communities revealing that bacteria and methanogens differ in their metabolic capacities. In both cDNA-based and DNA-based analysis, weighted UniFrac analysis (commonly present populations) revealed differences (P < 0.05) by treatment, week, and treatment � week in bacteria and archaea communities. Among methanogens, Methanosphaera and Methanobrevibacter differed between control and 3-NOP supplemented cows. Among bacteria, at the genus level, the most abundant lineages such as Prevotellaceae and Succinivibrionaceae increased at wk 4 and 8 and then declined whereas genera such as Lachnospiraceae and Ruminococcaceae followed a reverse pattern which correlated with the patterns observed for dissolved H2 concentrations. It can be concluded that whereas 3-NOP inhibited methanogens, its effect on certain bacteria was observed based on the hydrogen accumulated as a result of methane inhibition by 3-NOP and not by a direct effect on the bacteria themselves.

Keywords: enteric methane, rumen microbe, dairy cow.