Rumen and fecal microbiome of beef steers grazing endophyte-infected tall fescue - Fall 2023
Fescue toxicosis results from ingestion of tall fescue infected with the ergot alkaloid (EA)-producing endophyte Epichloe coenophiala. The gastrointestinal microbiota is the first point of interaction with EAs and may be modulated by them. To investigate this, rumen and fecal samples were collected from steers grazing toxic (E+) or non-toxic fescue for 14 days, followed by a pasture switch. Microbial communities were characterized using 16S rRNA amplicon sequencing (bacterial V4, archaeal V6-V8). Short-term E+ grazing did not affect alpha diversity, but beta diversity differed in rumen and feces, though communities largely overlapped between treatments. Relative abundance (RA) of dominant taxa remained unchanged, but low-abundance taxa were enriched in E+. In the rumen, these included proteolytic, amino acid decarboxylating, and methyl-compound forming microbes (e.g., Clostridia, Prevotellaceae, Lachnospiraceae (Butyrivibrio, Eubacterium), Streptococcaceae, and Gamma/Alphaproteobacteria), while fibrolytic taxa (e.g., Ruminococcus flavefaciens) declined. Hydrogenotrophic methanogens (Methanobrevibacter) decreased, while methylotrophic archaea and hydrogen-utilizing bacteria (e.g., Selenomonadaceae) increased, indicating altered hydrogen flow in the rumen. Similar subtle but significant shifts were observed in fecal communities, including members of Lachnospiraceae (Eubacterium) and Rikenellaceae (Mucinivorans). Comparable RA of core rumen and fecal microbiomes in previously exposed and never-exposed EA steers suggests no lasting effects. Short-term EA exposure selectively enriches taxa with adaptive metabolic functions, helping maintain rumen homeostasis under dietary stress.