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Appl Environ Microbiol. 2019 May 24. pii: AEM.00032-19. doi: 10.1128/AEM.00032-19. [Epub ahead of print]

Beef cattle fecal microbiota response to toxic tall fescue grazing.

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Interdisciplinary Toxicology Program Department of Physiology and Pharmacology Department of Crop and Soil Sciences, University of Georgia, Athens, GA.
Department of Bacteriology, University of Wisconsin - Madison, Madison, WI.
Department of Medicine, Division of Pulmonary, Allergy, and Critical Care Medicine, Emory University, Atlanta, GA.
Interdisciplinary Toxicology Program Department of Physiology and Pharmacology Department of Crop and Soil Sciences, University of Georgia, Athens, GA


Tall fescue, the predominant Southeastern United States cool season forage grass, frequently becomes infected with an ergot alkaloid-producing toxic endophyte, Epichlo√ę coenophialum Consumption of endophyte-infected fescue results in fescue toxicosis (FT), a condition that lowers beef cow productivity. Limited data on the influence of ergot alkaloids on rumen fermentation profiles or ruminal bacteria that could degrade the ergot alkaloids are available, but how FT influences the grazing bovine fecal microbiota, or what role fecal microbiota might play in FT etiology, and associated production losses, has yet to be investigated. Here, we used 16S rRNA gene sequencing of fecal samples from weaned Angus steers grazing toxic (n = 6; E+) or non-toxic (n = 6; Max-Q) tall fescue before, 1, 2, 14, and 28 days post-pasture assignment. Bacteria in the Firmicutes and Bacteroidetes phyla comprised 90% of the Max-Q and E+ steer fecal microbiota throughout the trial. Early decreases in the Erysipelotrichaceae family and delayed increases of the Ruminococcaceae and Lachnospiraceae families were among the major effects of E+ grazing. E+ also increased the abundances within the Planctomycetes, Chloroflexi, and Proteobacteria phyla and the Clostridiaceae family. Multiple operational taxonomic units classified to the Ruminococcaceae and Lachnospiraceae were correlated negatively with weight gains (lower in E+) and positively with respiration rates (increased by E+). These data provide insights into how E+ grazing alters the Angus steer microbiota and the relationship of fecal microbiota dynamics with FT.IMPORTANCE. Consumption of toxic endophyte-infected (E+) tall fescue has an estimated annual $1 billion negative impact on the U.S. beef industry, with one driver of these costs being lowered weight gains. As global agricultural demand continues to grow, mitigating production losses resultant from grazing the predominant Southeastern United States forage grass is of great value. Our investigation of the effects of E+ grazing on the fecal microbiota furthers our understanding of bovine fescue toxicosis in a real-world grazing production setting and provides a starting point for identifying easy-to-access fecal bacteria that could serve as potential biomarkers of animal productivity and/or FT severity for tall fescue grazing livestock.


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