Scope of Microbial Feed Additives in Ruminant Nutrition

The direct-fed microbials (DFM) are feed additives that are purported to contain only a source of naturally existing live microbes (bacteria, fungi, and/or yeast). In recent years, DFM have emerged as a potential biotherapeutic adjunct alternative to conventional antimicrobials following the ban or a strictly very limited usage of in-feed antibiotic growth promoters in the livestock industry. Bacteria such as lactic acid-producing bacteria, lactic acid-utilizing bacteria, as well as yeast like Saccharomyces spp. and fungi (Aspergillus spp.) are the commonly used microorganisms as DFM for ruminants. To date, the utilization of DFM has shown multifaceted benefits such as the ability to modulate the immune system, pH stabilization, establish balance in the gut microbial ecosystem, increase feed digestion, ruminal fermentation, improve nutrient utilization, and overall enhance the health and productivity of ruminants. Several researchers have also shown the beneficial effects of DFM in increasing growth performance and reduction of diarrheal incidences in young ruminants. Nevertheless, these positive findings are inconsistent across research, and their functional activities remain unexplored. More investigations are still needed to ascertain the mode of action of specific DFM in the gut of ruminants (cattle, buffaloes, sheep, and goats) in comparison to monogastric animals (pigs and poultry). In this context, the present chapter provides comprehensive insights into the effects of DFM on ruminants based on the scientific investigations carried out in the last 10 years as microbial feed additives. Furthermore, a brief discourse is also made on the challenges, potential barriers as well as safety aspects of DFM for ruminant industry.