The study was carried out on 24 cross-bred Brahman cattle in a 2x3 factorial design with two levels of concentrate supplement (0.5% and 1.5% body weight) and three supplemental sources (60 g soybean oil/kg DM, 60 g fish oil/kg DM and no supplement). Real-time PCR was applied to enumerate the presence of cellulolytic bacteria including Fibrobacter succinogenes, Ruminococcus albus and Ruminococcus flavefaciens and methanogens. It was shown that number of total bacteria, R. albus and R. flavefaciens remained unchanged over 90-day supplementation. However, F. succinogenes was influenced by the addition of both concentrate levels and soybean oil and fish fat with increasing number at the end of the trial (P