A Review of 3-Nitrooxypropanol for Enteric Methane Mitigation from Ruminant Livestock

SIMPLE SUMMARY: Enteric methane (CH(4)) from the anaerobic fermentation of feed carbohydrates in ruminant livestock accounts for 3 to 5% of global greenhouse gas emissions. Among the different CH(4) mitigating approaches evaluated to decrease enteric CH(4) emissions from ruminants, the feed additive 3-nitrooxypropanol is effective with a mean reduction in CH(4) of 30%, depending on animal type, diet and dose. 3-nitrooxypropanol is chemically synthesized and studies show low safety risk with no detrimental effects to animals and humans. 3-nitrooxypropanol was recently approved by regulatory authorities for use in Brazil and Chile and has received a favorable opinion from the scientific panel of the European Food Safety Authority, with approvals in various jurisdictions expected in the near future. As a substantial body of research on 3-nitrooxypropanol is now available, this review offers a timely analysis of the opportunities and challenges of using 3-nitrooxypropanol to mitigate enteric CH(4) emissions in ruminant livestock. ABSTRACT: Methane (CH(4)) from enteric fermentation accounts for 3 to 5% of global anthropogenic greenhouse gas emissions, which contribute to climate change. Cost-effective strategies are needed to reduce feed energy losses as enteric CH(4) while improving ruminant production efficiency. Mitigation strategies need to be environmentally friendly, easily adopted by producers and accepted by consumers. However, few sustainable CH(4) mitigation approaches are available. Recent studies show that the chemically synthesized CH(4) inhibitor 3-nitrooxypropanol is one of the most effective approaches for enteric CH(4) abatement. 3-nitrooxypropanol specifically targets the methyl-coenzyme M reductase and inhibits the final catalytic step in methanogenesis in rumen archaea. Providing 3-nitrooxypropanol to dairy and beef cattle in research studies has consistently decreased enteric CH(4) production by 30% on average, with reductions as high as 82% in some cases. Efficacy is positively related to 3-NOP dose and negatively affected by neutral detergent fiber concentration of the diet, with greater responses in dairy compared with beef cattle when compared at the same dose. This review collates the current literature on 3-nitrooxypropanol and examines the overall findings of meta-analyses and individual studies to provide a synthesis of science-based information on the use of 3-nitrooxypropanol for CH(4) abatement. The intent is to help guide commercial adoption at the farm level in the future. There is a significant body of peer-reviewed scientific literature to indicate that 3-nitrooxypropanol is effective and safe when incorporated into total mixed rations, but further research is required to fully understand the long-term effects and the interactions with other CH(4) mitigating compounds.