Rumen microbial predictors for short-chain fatty acid levels and the grass-fed regimen in angus cattle

Authors: LIU, JIANAN - University Of Maryland; BAI, YING - Heibei University Of Engineering; LIU, FANG - University Of Maryland; KOHN, RICHARD - University Of Maryland; TADESSE, DANIEL - Food And Drug Administration(FDA); SARRIA, SAUL - Food And Drug Administration(FDA); Li, Robert; SONG, JIUZHOU - University Of Maryland

Submitted to: Animals
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2022
Publication Date: 10/31/2022
Citation: Liu, J., Bai, Y., Liu, F., Kohn, R.A., Tadesse, D.A., Sarria, S., Li, R.W., Song, J. 2022. Rumen microbial predictors for short-chain fatty acid levels and the grass-fed regimen in angus cattle. Animals. 12(21). Article 2995. https://doi.org/10.3390/ani12212995.
DOI: https://doi.org/10.3390/ani12212995

Interpretive Summary: The grass-fed beef production represents one of the fastest growth segments of the cattle industry due to the increased consumer consciousness for healthy beef products and animal welfare and environmentally friendly animal production. However, the similarity and difference in rumen microbial composition and species interaction between grass-fed and grain-fed cattle have not been systemically evaluated. Furthermore, biomarkers associated with the grass-fed regimen have yet to be identified. In this study, we compared the rumen metabolite and microbial features of Angus steers raised under the two feeding schemes and identified metabolite and microbial signatures with high predictive power for grass-fed cattle. Our findings will have pragmatic implications for enhancing production efficiency in the grass feeding regimen.

Technical Abstract: The health benefits of grass-fed beef are well documented. However, the rumen microbiome features in beef steers raised in the grass-fed regimen have yet to be identified. This study examined the effect of grass- vs. grain-fed on the microbiome and rumen fermentation profile of beef steers. Our findings show that the rumen microbiome of the grass-fed cattle demonstrated greater species diversity harbored significantly higher microbial alpha diversity, including multiple species richness and evenness indices, than grain-fed cattle (P < 0.0001) than that of the grain-fed cattle. Global network analysis unveiled that grass-fed cattle's rumen microbial interaction networks had higher modularity, suggesting a more resilient and stable microbial community under this feeding regimen. Using the analysis of compositions of microbiomes with a bias correction (ANCOM-BC) algorithm, the abundance of multiple unclassified genera, such as those belonging to Planctomycetes, LD1-PB3, and SR1, as well as Lachnospira, and Sutterella was significantly enriched in the rumen of grass-fed steers. Sutterella was also the important genus able to distinguish the two feeding regimens by Random Forest. A rumen microbial predictor consisting of an unclassified genus in the candidate division SR1 (numerator) and an unclassified genus in the order Bacteroidales (denominator) accurately distinguished the two feeding schemes. Multiple microbial signatures or balances showed strongly correlated with various levels of SCFA in the rumen. For example, a balance represented by the log abundance ratio of Sutterella to Desulfovibrio was strongly correlated with acetate to propionate ratios in the rumen (R2 = 0.87), which has the potential to be developed as a valuable biomarker for optimizing milk fat yield and cattle growth. Therefore, our findings provided novel insights into microbial interactions in the rumen under different feed schemes and their ecophysiological implications. The new knowledge will be conducive to developing rumen manipulation strategies to improve feed conversion ratios and average daily weight gains for the grass- or pasture-fed cattle production.