“…Rumen inhabits several microbial populations, that is, bacteria, protozoa, fungi, bacteriophages, yeasts, and methanogens symbiotically, which are very dynamic, plastic, and redundant in function with the changes in diets though core microbiota persists, which has probably evolved by host-microbiota interaction in the evolutionary pressure over thousands of years [1]. A symbiotic relationship exists between rumen microbes and host animals in which both provide desirable substrates to each other mainly through these ways-1) physical breakdown of feed particles by mastication and rumination expands their surface area for microbial attachment and degradation, and consequently, microbes secrete various enzymes for dietary substrate degradation, 2) ruminal movements bring microbes in contact with the dietary substrate by mixing of digesta and consequently produce fermentation products (e.g., H 2 , CO 2 , ammonia, short-chain fatty acids (SCFAs), and 3) utilization (absorption and consumption) of the fermentation products for keeping optimal ruminal conditions (e.g., pH) to maintain microbial growth and microbial protein synthesis [2].…”