Effect of concentrate levels on the abundance of some rumen organisms in feedlot Nellore cattle determined by qPCR

Abstract This study aimed to evaluate the effects of concentrate levels (CL) (45 to 90% on a dry matter basis) on the abundance of some species of cultured-rumen bacterial, protozoa, and Archaea in four rumen-fitted Nellore cattle. Species-designated primers were used to quantify rumen bacteria, while group and Domain-specific primers were used to quantify protozoa and Archaea by qPCR. CL caused a tendency of quadratic effect (p = 0.067) in the abundance of Fibrobacter succinogenes , while the abundance of Ruminococcus albus (p = 0.003) and Selenomans ruminantium (p = 0.006) presented a linear increase according to CL. Prevotella ruminicola abundance was quadratically affected by CL (p = 0.005), and Streptococcus bovis demonstrated a tendency of linear decrease (p = 0.076). There was no effect of CL in the abundance of Archaea (p = 0.248), but there was a quadratic effect in the abundance of protozoa (p = 0.033). The increase in CL from 45 to 90% for feedlot cattle promoted significant changes in the abundance of some species of bacteria and protozoa. However, these changes were more abrupt than reported in the literature because the changes in the diets were made progressively. Thus, a progressive increase in CL seems to cause few disturbances in the abundance of cultured rumen bacteria.