Abstract
Simple Summary: Enteric methane (CH4) from the anaerobic fermentation of feed carbohydrates in ruminant livestock accounts for 3 to 5% of global greenhouse gas emissions. Among the different CH4 mitigating approaches evaluated to decrease enteric CH4 emissions from ruminants, the feed additive 3-nitrooxypropanol is effective with a mean reduction in CH4 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 CH4 emissions in ruminant livestock. Abstract: Methane (CH4) 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 CH4 while improving ruminant production efficiency. Mitigation strategies need to be environmentally friendly, easily adopted by producers and accepted by consumers. However, few sustainable CH4 mitigation approaches are available. Recent studies show that the chemically synthesized CH4 inhibitor 3-nitrooxypropanol is one of the most effective approaches for enteric CH4 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 CH4 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 CH4 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 CH4 mitigating compounds.
Generated Summary
This review article examines the use of 3-nitrooxypropanol (3-NOP) as a feed additive to mitigate enteric methane (CH4) emissions from ruminant livestock. The study involved an analysis of existing literature, including meta-analyses and individual studies, to provide a comprehensive overview of the opportunities and challenges associated with using 3-NOP in livestock production. The focus was on understanding how 3-NOP reduces CH4 emissions, its effects on rumen fermentation, animal productivity, and the practical considerations for its use in farming. The study includes an overview of 3-NOP’s mechanism of action, safety, and efficacy, intending to provide science-based information for commercial adoption and to guide informed decisions by farmers and technical advisors.
Key Findings & Statistics
- Enteric methane (CH4) from ruminant livestock accounts for 3 to 5% of global greenhouse gas emissions.
- The feed additive 3-nitrooxypropanol is effective with a mean reduction in CH4 of 30%, depending on animal type, diet, and dose.
- 3-nitrooxypropanol specifically targets the methyl-coenzyme M reductase and inhibits the final catalytic step in methanogenesis in rumen archaea.
- 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.
- 3-NOP decreases enteric CH4 emissions in a dose-response manner.
- In the meta-analysis of Dijkstra et al. (2018) from 11 studies, the average 3-NOP dose used in beef cattle was 144 mg/kg of DM, ranging from 50 to 345 mg/kg of DM; in dairy cattle, the average dose was 81 mg/kg of DM, ranging from 27 to 135 mg/kg of DM.
- Several meta-analyses report that increasing dosage level of 3-NOP linearly decreased enteric CH4 emissions.
- In dairy cattle, CH4 (g/d) decreased on average over the study by 26 to 28% with 3-NOP (40 to 80 mg/kg feed DMI), and this effect did not diminish over time.
- In a 34-week feeding study by Vyas et al. (2016), supplementation of 3-NOP at 200 mg/kg DM decreased, on average, emission of enteric CH4 (g/d) by 82% in feedlot finishing beef cattle.
- In a beef cattle feedlot study by McGinn et al. (2019), there was a small, constant decline in CH4 emission reduction (from 80% to 60% reduction over 90 d).
Other Important Findings
- 3-NOP increases the calories available from feed to the cow.
- Over time the methane producing bacteria are starved and thus reduce the gut, so the stuff also takes a bit of time to reach full effect – i think 6-8 weeks as per the paper.
- There are reduced methane bacteria as part of the mechanism.
- Positive dose response as per this paper so adding more has a higher effect.
- The compound 3-NOP was first chemically synthesised by Ogawa et al. (1990), and a patent was granted for the use of 3-NOP as a CH4 mitigant.
- 3-NOP is highly soluble and rapidly metabolized in the rumen to very low concentrations of nitrate, nitrite and 1,3-propanediol.
- 3-NOP specifically binds into MCR and inactivates the enzyme by temporarily oxidizing the nickel ion from oxidation state (+1) to (+2) in the active site, leading to an inhibition of methanogenesis.
- Most studies showed no effect of 3-NOP on ammonia N concentration, except when a high level of 3-NOP was used.
- Incorporating 3-NOP into a ration or a component of the ration (concentrate, forage), appears to lead to a more continuous presence in the rumen as animals consume their feed throughout the day.
- The world’s increasing demand for animal-sourced protein products will undoubtedly cause enteric CH4 emissions to increase unless mitigation is adopted.
- In 5 long-term experiments, CH4 yield (g/kg DM) was significantly linearly (R2 = 0.91, n = 19, p < 0.01) decreased with increasing level of 3-NOP addition.
- The effects of 3-NOP on DMI appear to be different among studies and may depend on dose, animal type, diet and the duration of feeding.
- In the meta-analysis of Kim et al. (2020) from 14 beef cattle studies, DMI tended to decrease (slope = −0.0016, p = 0.06, and R2 = 0.17) as the dose of 3-NOP supplemented increased.
- In dairy cattle studies, feeding 3-NOP increased milk protein (g/100 g of milk) and milk fat content (g/100 g of milk) by up to 8%.
Limitations Noted in the Document
- Many of these studies are short-term and even the long-term studies have been limited to several months in duration.
- No published study has examined the effects of feeding 3-NOP over multiple lactations or seasons.
- Further information on using 3-NOP under a broad range of feeding systems is still needed.
- The potential for adaptation of the rumen microbiome such that compounds diminish in effectiveness has been shown with other rumen modifying compounds (e.g., ionophores, essential oils, etc.).
- The high starch concentration of beef cattle finishing diets results in a rumen fermentation with greater molar proportion of propionate, compared with dairy cattle.
- Studies with repeated measurements over the feeding period and over multiple years for mature beef cows and over multiple lactations for dairy cows are needed to ensure the mitigation effect of 3-NOP is persistant.
Conclusion
In conclusion, the review highlights the significant potential of 3-nitrooxypropanol (3-NOP) as a methane mitigation strategy in ruminant livestock. The compound effectively inhibits enteric CH4 emissions by targeting the methyl-coenzyme M reductase enzyme, with a mean reduction of 30% in CH4 emissions. Furthermore, 3-NOP has shown promising safety profiles in animals, and has been approved for use in several regions. The review underlines the importance of long-term studies to fully understand the sustained efficacy of 3-NOP and its interaction with various diets and animal types. While 3-NOP is effective in reducing CH4 emissions, further research is needed to explore its effects over multiple lactations and seasons, which are important for the long-term adoption of 3-NOP. The review emphasizes the need to consider the broader environmental impacts of 3-NOP, particularly the potential for unintended consequences on other emissions, such as manure CH4 emissions. The widespread adoption of 3-NOP in ruminant diets represents a significant step forward in offering livestock producers a practical tool for lowering CH4 emissions. It suggests further research should focus on its use in grazing animals and long-term effectiveness to ensure the sustainability and broader environmental benefits of 3-NOP.