“…The adequate amount of dietary crude protein (CP) could promote ruminal microbial growth and production performance of animals (Argyle & Baldwin, 1989;Atasoglu, Newbold, & Wallace, 2001). Numerous studies reported that increasing dietary CP level improved dry matter (DM) intake, nutrient digestibility (Chanthakhoun, Wanapat, & Berg, 2012;Weigel, Elliott, & Clark, 1997), ruminal fermentation (Granzin & Dryden, 2002;Weigel et al, 1997), microbial protein synthesis and ruminal bacterial populations (Granzin & Dryden, 2002). Nevertheless, no literature reported the effects of different dietary CP levels on populations of Ruminococcus albus, Ruminococcus flavefaciens, Fibrobacter succinogenes, Butyrivibrio fibrisolvens, Prevotella ruminicola and Ruminobacter amylophilus as well as activities of carboxymethylcellulase, cellobiase, xylanase, pectinase, α-amylase and protease in steers.…”