Advancements in Methane-Mitigating Feed Additives in Ruminants

Ruminant animals are responsible for substantial enteric methane (CH4) emission, which arises from normal fermentation of feeds in the rumen. Therefore, ruminant livestock is considered a significant driver of climatic change. Over the last two decades, many research works have been intensively performed by different stakeholders to better understand the mechanisms of methanogenesis, uncover the molecular biology of methanogens, and develop various CH4-mitigation technologies, including chemical, biological, and natural phytochemicals to be used as feed additives to inhibit methanogenesis. Only a few CH4-mitigating agents were known before the year 2000, but many feed additives with CH4 inhibition effects are recognized, and their responses have been well-studied. Phytochemicals have additional benefits due to the presence of antioxidant and immune-modulating properties, which can improve health and ameliorate stress besides inhibiting CH4 production. It seems different CH4-mitigating agents with complementary mode of actions and various phytochemical mixtures would be more practical as these approaches would provide greater inhibition effects on methanogenesis and would likely lose the effectiveness over time due to lesser adaptability of the ruminal microbiota to these agents when used in combination. This chapter discusses some encouraging agents, which potentially lower methanogenesis, while also improving productive performance and nutrient utilization, and hence could be possibly applied at farm levels.