Todd R. Callaway

The rumen is the largest of the four chambers of the “stomach” in ruminant animals, which harbors an incredibly dense, diverse, and dynamic microbial community crucial for feedstuff degradation, animal health, and production. The primary objective of this article is to enhance knowledge and comprehension of rumen microbiology by providing an introductory-level overview of the field of rumen microbiology. Ruminants possess a distinctive digestive system optimized for the microbial breakdown of complex plant materials. The ruminant ”stomach” consists of four chambers (e.g., reticulum, rumen, omasum, and abomasum), which is home to a microbial population that degrades feedstuffs consumed by ruminant animals. Dr. Robert Hungate and Dr. Marvin Bryant’s groundbreaking research in the 1960s laid the foundation for understanding the function of the ruminal microbial ecosystem. Recent advancements (e.g., next-generation sequencing) have provided the field with deeper insight into populations, boosting our understanding of how the microbial population of the rumen functions in a variety of conditions. The ruminal microbial ecosystem is comprised of bacteria, along with archaea, protozoa, bacteriophage, and fungi, each contributing to the symbiotic relationship between the microbial ecosystem and the host animal that is essential for optimal animal health and efficient animal production. Traditional anaerobic growth techniques have facilitated the study of individual anaerobic bacteria but have been limited by dependence on growth in laboratory conditions. The development of 16S rRNA sequencing allows the identification of microbial populations that cannot be grown and allows an unbiased view of microbial diversity. Diet shapes the rumen microbial population composition, influencing animal production metrics such as feed efficiency, methane emissions, and immunological functions. Feed additives (e.g., essential oils, eubiotics) hold promise by manipulating and unraveling the microbial biochemical potential for improving animal health, feed efficiency, environmental impacts, and overall production sustainability. Future research impacts include the development of probiotics, prebiotics, and genetic strategies for optimizing the rumen microbiome’s multifaceted impacts.

Livestock producers need new technologies to maintain the optimal health and well-being of their animals while minimizing the risks of propagating and disseminating pathogenic and antimicrobial-resistant bacteria to humans or other animals. Where possible, these interventions should contribute to the efficiency and profitability of animal production to avoid passing costs on to consumers. In this study, we examined the potential of nitroethane, 3-nitro-1-propionate, ethyl nitroacetate, taurine and L-cysteinesulfinic acid to modulate rumen methane production, a digestive inefficiency that results in the loss of up to 12% of the host’s dietary energy intake and a major contributor of methane as a greenhouse gas to the atmosphere. The potential for these compounds to inhibit the foodborne pathogens, Escherichia coli O157:H7 and Salmonella Typhimurium DT104, was also tested. The results from the present study revealed that anaerobically grown O157:H7 and DT104 treated with the methanogenic inhibitor, ethyl nitroacetate, at concentrations of 3 and 9 mM had decreased (p < 0.05) mean specific growth rates of O157:H7 (by 22 to 36%) and of DT104 (by 16 to 26%) when compared to controls (0.823 and 0.886 h−1, respectively). The growth rates of O157:H7 and DT104 were decreased (p < 0.05) from controls by 31 to 73% and by 41 to 78% by α-lipoic acid, which we also found to inhibit in vitro rumen methanogenesis up to 66% (p < 0.05). Ethyl nitroacetate was mainly bacteriostatic, whereas 9 mM α-lipoic acid decreased (p < 0.05) maximal optical densities (measured at 600 nm) of O157:H7 and DT104 by 25 and 42% compared to controls (0.448 and 0.451, respectively). In the present study, the other oxidized nitro and organosulfur compounds were neither antimicrobial nor anti-methanogenic.