Context: Source and composition of feed influence rumen microbial community which determine efficiency of feed digestion and thus productivity in ruminants.  Therefore, changes in the structure, function and diversity of the rumen microbial populations in response to changes in diet provide an understanding in the rumen fermentation process.

Aims: This study, consisted of two experiments, was conducted to determine the effects of supplementing different protein and energy sources on the rumen bacterial community in cattle.

Methods: The dietary treatments of the first experiment which evaluated the effect of protein sources were: i) Hymenachne acutigluma grass, rice straw and rice bran (1.5 kg/head/d) assigned as C1, ii) C1 plus 120 g urea/head/d (C1+U), iii) C1 plus 720 g soybean/head/d (C1+SM), and iv) C1 plus 720 g of blood and feather meal (in 1:1 ratio)/head/d (C1+BFM). The treatments in the second experiment were: i) Hymenachne acutigluma grass, rice straw and concentrate (1.5 kg/head/d) assigned as C2, ii) C2 plus 250 g fish oil/head/d (C2+FO) and iii) C2 + 250 g soybean oil/head/d (C2+SO). At the end of the 90-day feeding trial, rumen fluids were extracted for microbial DNA isolation to identify the microbe species by PCR-DGGE method and sequencing of 16S rRNA region.

Key results: The sequences of some DNA bands were closely related to the bacteria strains of the Prevotella, Cytophaga, Capnocytophaga, Cyanobacterium, Catonella, Faecalibacterium, Lachnospiraceae, Ruminococcaceae, Propionivibrio, Galbibacter, Moorellaglycerin, Escherichia coli and Klebsiella alba groups with similarity levels ranging from 73% to 96%. In addition, the Prevotella species was found in both the protein and the energy supplement trials, and irrespective of diet supplements, the Firmicutes and Bacteroidetes were the prominent groups in the rumen.

Conclusions: Firmicutes and Bacteroidetes are the two dominant groups of rumen microflora, and Bacteroidia and Clostridia classes together with the Prevotella genus are predominant in the rumen irrespective of protein and energy sources.

Implications: Our findings provide evidence on the effect of diet on the interaction of rumen microbial community and have important implications in establishing optimal diets for cattle.

Keywords: cattle; energy; protein; rumen microbial community; supplementation