Temporal stability of the rumen microbiota

The stability of the rumen microbial community was determined as part of a study assessing the effect of basal diet and supplementation on feed efficiency and methane production in beef cattle. Subgroups of 50 beef steers were fed either of two diet formulations consisting of approximately 10:90 or 50:50 forage:concentrate ratios respectively. Supplements of a high oil feed by-product and nitrate, were added either individually or in combination. Digesta samples were taken at time points over ~200 days during the finishing phase of the cattle. In total, 313 16S rRNA gene amplicon libraries were prepared and sequenced.Bray Curtis dissimilarity was used to determine clustering of the microbial communities. Analysis of molecular variance (AMOVA) revealed highly significant (p<0.001) differences in microbial diversity between cattle fed different basal diets, driven by increased relative abundance of an unclassified Gammaproteobacteria OTU in the high concentrate fed animals. Within basal diet groups, addition of the nitrate and combined supplements had a significant effect compared to pre-treatment time points and controls. Recorded methane emissions were significantly lower in these animals as a possible consequence of microbial metabolism reducing H2 availability. Predicted functional analysis revealed increased relative abundance of succinate metabolism genes in concentrate fed animals.Measurements of the stability and response of the microbial community over the time course of the experiment showed continuing adaptation for >25 days in the high concentrate groups. After this time point, however, no significant variability was detected. This result indicated that, once adapted to a change in diet, the rumen microbial community remains in a relatively stable alternate state.