Q-304. Adaptation of Non-Archaeal Prokaryotic Rumen Populations when Monensin Is Used to Reduce Methane Emissions

J. J. Bouchard, K. M. Wittenberg, K. H. Ominski, D. O. Krause;
Univ. of Manitoba, Winnipeg, MB, CANADA.

Background: Methane production by cattle contributes to greenhouse gas emissions and the Gram-positive ionophore antibiotic, monensin, may be an effective mitigant. However, most cattle production studies have been short-term (one month). We previously conducted a long-term (four month) study in which cattle (10 per group) were fed either a high grain or high forage diet with or without monensin. Methane emissions were measured using the SF6 technique and there was an initial reduction in methane followed by a return to baseline levels. We hypothesized that non-methane producing rumen bacteria were adapting to monensin in the rumen and thus altering the flow of reducing equivalents available to methanogens. Here we describe microbial population changes using terminal restriction fragment length polymorphism analysis (TRFLP) of 16S rDNA. Methods: We attained terminal restriction fragments (TRF) from rumen fluid samples for each of the four diets. TRFs were evaluated using a series of bioinformatic tools: (MiCA, PAT, and RDP) enabling us to determine a relationship between a specific TRF, a Genbank Accession Number, and a taxonomic group. Results: The most significant (P < 0.05) changes occurred in the Gram-positive Firmicutes phylum. Diet (forage vs concentrate), not monensin, had the greatest effect on the number of TRFs. Throughout the four month study, within the phylum Firmicutes the class Bacilli increased (P < 0.05) in diversity with the concentrate diets, but decreased (P < 0.05) in diversity in the forage diet. In contrast, the class Clostridia within the phylum Firmicutes increased (P < 0.05) in diversity in the forage diet and declined (P < 0.05) in the concentrate diet over time. Monensin decreased (P < 0.05) TRF diversity in the Bacilli and Clostridia, but it was short term. Conclusions: This data suggests that carbohydrate fermentability (forage vs concentrate) had the greatest influence on Firmicute diversity. However, given that monensin is a Gram-positive antibiotic, and that we found signficant changes in the Bacilli and Clostridia, the contribution of these two groups is likely to be substantial during monensin adaptation.