**2. Major rumen microbes**

At any time there are billions of any species of anaerobic bacteria and facultative anaerobic bacteria residing in rumen along with a mixed population of various anaerobic protozoa, anaerobic fungi and flagellates making it a diverse microbial consortium in nature. The bacteria along with protozoa make most of the microbial mass (nearly 80%) inside rumen. The bacteria present in specialized niches are a very small fraction that cannot be recovered by cultural methods and even among cultivable bacteria true number of diversity is now revealed only by molecular techniques [6]. The bacteria can further be cellulolytic (fiber digesting), amylolytic (starch and sugar digesting) and lactate utilizing bacteria. The role of symbiotic microbial ecosystem consisting of bacteria, protozoa and fungi is of great significance in ruminants. Phylum Euryarchaeota within domain *Archaea* includes 7 orders—*Methanobacteriales*, *Methanomicrobiales*, *Methanococcales*, *Methanopyrales*, *Methanocellales*, *Methanosarcinales* and *Methanomassiliicoccales*. The orders are further divided into 10 families and 31 genera [7–9].
