Effective Methane Mitigation Strategies in Livestock Production for a Sustainable Future

Co-author: Ishaya Gadzama

Reflecting on Our Planet: The Impact of Human Activities on Earth's Health

Just fifty years ago, the Apollo mission ventured to the moon, offering us a unique perspective to look back at our own planet. In this time frame, the human population has doubled, creating a greater demand for resources and a drive to produce more, often with little consideration for our environment. Comparing images of Earth from then to now reveals how our activities have significantly altered the planet. Human beings have threatened Earth’s health due to inadequate planning and human error. For the first time in history, the stability of humans and nature cannot be taken for granted. Industrialization has disrupted the ten thousand years of the Holocene, a period of stable temperatures that allowed optimal conditions for life. Moreover, we are pushing the boundaries of biomass, biodiversity, freshwater, and nutrient recycling due to our activities, including livestock production. Globally, agricultural livestock accounts for about 9% of total anthropogenic greenhouse gas (GHG) emissions [1]. However, the natural world is resilient and can recover with our help. While individual human activities might seem negligible, their interconnectedness leads to serious problems. It is crucial to find ways to relate to our environment better and reverse these negative impacts. We can help restore the balance and ensure a healthier planet for future generations by adopting sustainable practices and making conscious efforts to reduce our ecological footprint.

The Impact of Greenhouse Gases on Livestock Production

The two primary GHGs linked to ruminant production are methane (CH₄) and nitrous oxide (N2O). While methane has a shorter lifespan in the atmosphere compared to carbon dioxide, its warming effect is far greater. The main sources of methane in ruminant production are enteric fermentation (digestive processes) and manure management. On the other hand, nitrous oxide is primarily released during manure treatment. Nitrous oxide is a particularly potent GHG, with a global warming potential approximately 270 times that of carbon dioxide, and it persists in the atmosphere for over a century [2]. The continuous rise in GHG concentrations in the atmosphere is a major driver of global warming, and livestock production is a significant contributor to these emissions. 

Enhancing Livestock Production to Meet Growing Demands and Mitigating Climate Change

As the global population is projected to increase by 9.7 billion by 2050, there is an urgent need to improve livestock production to meet this growing demand while mitigating the climate change impacts caused by livestock farming. Enhancing livestock productivity is essential to ensure food security and environmental sustainability. Emissions per unit of livestock product can be reduced by either increasing the efficiency of the animal production system or by directly addressing the sources of emissions. Significant advancements have been made in developed countries to improve the efficiency of livestock. However, in developing countries, there is still much work to be done to enhance animal production, particularly for ruminants. 

Rumen Fermentation and Methane Mitigation Strategies

In the rumen, a complex community of microorganisms breaks down feed, producing volatile fatty acids (VFAs) as the primary energy source for the animal. Methanogens, a type of archaea, utilize hydrogen (H₂) produced during fermentation to produce methane as a byproduct. Therefore, methane mitigation strategies aim to either reduce H2 availability for methanogens or directly inhibit their activity. This can be achieved through various approaches, including feed manipulation to shift fermentation towards propionate production (an alternative H₂ sink), using additives like ionophores to inhibit H2-producing bacteria, and supplementing with direct-fed microbials (DFMs) such as propionic acid bacteria (PAB) that compete with methanogens for H₂. Furthermore, exploring alternative H2 sinks like acetogenesis and the direct utilization of methane by methane-oxidizing bacteria (MOB) hold promise for future mitigation strategies [5]. 

Nutritional manipulation is one of the straightforward, most effective and inexpensive strategies to reduce greenhouse gas emissions from ruminant production systems [3,4,5]. This strategy alone could curtail up to 70% of ruminant methane emissions, depending on the method or nature of the nutritional intervention [6,7]. A variety of other strategies to mitigate enteric methane emissions from ruminant animals are presented below.

Enteric Methane Emission Mitigation Strategies

Feed Manipulation

• Advantages: Reduces enteric methane levels by up to 70%. High-quality forage containing more fermentable carbohydrates, less non-digestible fiber (NDF), and a lower carbon-to-nitrogen ratio ensures higher digestibility, directing rumen fermentation towards propionate.
• Disadvantages: High levels of concentrate in feed can lead to health disorders such as subacute ruminal acidosis (SARA) due to elevated lactic acid and volatile fatty acids concentration in the rumen.
• Way Forward/Solution: Change the type or quality of forage or adjust the concentrate-to-forage ratio in the feed. Use younger plants with higher fermentable carbohydrates, less non-digestible fiber, and a lower C:N ratio to improve digestibility and passage rate, directing rumen fermentation towards propionate.

Ionophores

• Advantages: Enhances energy metabolism efficiency, improves ruminal nitrogen metabolism, reduces the risk of bloating and acidosis, and modulates the ratio of propionic to acetic acid production, resulting in body weight gain.
• Disadvantages: Impairs dry matter intake in dairy cows and beef steers. Effectiveness decreases over time due to adaptation by ciliate protozoa and resistance development in succinate- and propionate-producing bacteria.
• Way Forward/Solution: Conduct further research to address the issue of waning effectiveness caused by microbial adaptation and resistance development.

Methanogenesis Inhibitors

• Advantages: Exhibit remarkable inhibitory capacity against methanogens. Certain inhibitors, such as 3-NOP, do not affect daily weight gain, dry matter intake, milk production, or digestibility.
• Disadvantages: Gradual decrease in effectiveness as resistant microbes replace sensitive ones. Hydrogen accumulation inside the rumen presents unknown long-term effects. High costs and safety concerns limit practical applications.
• Way Forward/Solution: Investigate the long-term effects of hydrogen accumulation and explore cost-effective and safer alternatives.

Essential Oils and Plant Extracts

• Advantages: Possess broad-spectrum antimicrobial properties and are generally considered safe for consumption. These additives can promote or inhibit specific groups of microorganisms, including methanogens.
• Disadvantages: Effectiveness varies depending on the plant source and dosage. Certain extracts, such as tannins, may negatively impact protein digestion.
• Way Forward/Solution: Optimize dosages and combinations to maximize methane reduction while minimizing adverse effects. Explore new plant sources with potent anti-methanogenic properties.

Biochar

• Advantages: Improves growth and blood profiles while exhibiting inhibitory effects against rumen pathogens.
• Disadvantages: Limited research on long-term effects and optimal application methods in ruminant diets.
• Way Forward/Solution: Conduct further research on the long-term effects, optimal application methods, and potential for large-scale production and utilization.

Seaweeds

• Advantages: Exhibit anti-methanogenic properties, particularly species such as Asparagopsis taxiformis and Asparagopsis armata, which can reduce methane emissions by 50% to over 80% in cattle.
• Disadvantages: Potential for negative impacts on dry matter intake (DMI), animal health, or product quality if not appropriately processed or dosed.
• Way Forward/Solution: Optimize seaweed species, processing methods, and dosages to maximize methane reduction while ensuring animal safety and product quality. Investigate the sustainability and scalability of seaweed cultivation for feed.

Prebiotics

• Advantages: Modify the rumen bacterial community structure, thereby limiting methane emissions.
• Disadvantages: Limited usage compared to other feed additives.
• Way Forward/Solution: Conduct more research to understand the mechanisms of action and optimize prebiotic types and dosages for effective methane reduction.

Propionic Acid Bacteria (PAB)

• Advantages: Produce propionate by utilizing hydrogen, reducing its availability for methane production.
• Disadvantages: Fail to persist in the rumen of cattle fed high-starch diets due to reduced efficacy from increased propionate production.
• Way Forward/Solution: Develop strategies to enhance the persistence and colonization of PAB in the rumen, particularly in high-starch diets. Explore alternative PAB strains with greater resilience and methane-reducing potential.

Acetogens

• Advantages: Utilize hydrogen and carbon dioxide to produce acetate, providing an alternative hydrogen sink.
• Disadvantages: Have lower abundance and hydrogen affinity compared to hydrogenotrophic methanogens, limiting their competitiveness for hydrogen disposal.
• Way Forward/Solution: Investigate strategies to increase the abundance and hydrogen affinity of acetogens in the rumen, potentially through genetic engineering or targeted delivery systems.

Methane-oxidizing bacteria (MOB)

• Advantages: Directly utilize methane generated during ruminal fermentation.
• Disadvantages: Limited in vivo studies on using MOBs as probiotics.
• Way Forward/Solution: Conduct more research on isolating, screening, and evaluating the efficacy of MOBs as probiotics in reducing methane emissions while enhancing animal nutrition in vivo. Explore methods to improve MOB colonization and activity in the rumen.
  

Conclusion

As the global demand for meat and milk products continues to rise, mitigating enteric methane emissions from ruminant animals is crucial for sustainable agriculture and climate change mitigation.

References

1. Intergovernmental Panel on Climate Change (2007). Climate change 2007: The physical science basis. Contribution of Working Group I to the Fourth Assessment Report of the IPCC. Retrieved December 21, 2008, from http://www.ipcc.ch/ipccreports/ar4-wg1.htm
2. Food and Agriculture Organization of the United Nations (2006). Livestock a major threat to the environment: Remedies urgently needed. Retrieved from http://www.fao.org/newsroom/en/news/2006/1000448/index.html
3. Kebreab, E., Strathe, A., Fadel, J., Moraes, L., & France, J. (2010). Impact of dietary manipulation on nutrient flows and greenhouse gas emissions in cattle. Revista Brasileira de Zootecnia, 39, 458-464.
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