'Geophagy' and Clay Minerals: Influencing Ruminal Microbial Fermentation for Methane Mitigation.

Methane is a greenhouse gas with high warming potential, and ruminants like cattle and sheep are a major source of its emission. In the rumen, the first stomach compartment, diverse microorganisms and fauna live, including archaea, bacteria, protozoa, nematodes, and fungi. They participate in complex fermentation processes. During rumen fermentation, various gases are produced, dominantly hydrogen and carbon dioxide. In methanogenesis, methanogens utilize these two gases to produce methane as a byproduct, which burps out into the atmosphere. Therefore, interfering with this methanogenesis is a promising way of reducing methane. Supplementing feed containing clay minerals could be one of method to do so as ruminants naturally consume them as they graze, often called "geophagy". This review discusses the role of clay minerals in enteric methane abatement, emphasizing the clay-microbial interaction in the rumen. In these interactions, clay minerals also serve as a carrier for other chemicals and influence microbial attachment. Elemental dissolution and cations from clay mineral and their buffering capacity can further influence microbial dynamics in rumen fluids. By combining insights from microbiology, soil science, and animal nutrition, this review provides an interdisciplinary view of rumen interactions. Findings from this review can help to develop a low-cost and safe clay feed supplement to reduce livestock methane emissions.