150 bp index run. Cellulolytic ruminal bacteria including Fibrobacter succinogenes, Ruminococcus albus, and R. bicirculans were reduced by an induced acidotic challenge. Up to 68 functional genes were differentially expressed between the two treatments. Genes mapped to carbohydrate, amino acid, energy, vitamin and co-factor metabolism pathways, and bacterial biofilm formation pathways were enriched in beef cattle challenged with sub-acute acidosis. This study reveals transcriptionally active taxa and metabolic pathways of rumen microbiota during induced acidotic challenge.