The Road to Net Zero Livestock Production

Introduction

The global agricultural sector, including associated land-use changes, was responsible for emitting 10.6 gigatons (Gt) of carbon dioxide equivalent (CO₂e), contributing considerably to the overall 53 Gt CO₂e of global greenhouse gas (GHG) emissions (FAO, 2023). In the United States, the agriculture sector contributed 0.59 Gt CO₂e in 2022, representing 9.36% of the nation's GHG emissions. This marked a 7.7% increase from 1990 levels but a 2% decrease from the previous year (EPA, 2024). Methane (CH₄) and nitrous oxide (N₂O), as the primary non-CO₂ GHGs, were responsible for 58.4% and 52.1% of global emissions, respectively, with enteric fermentation and manure management being significant contributors to global anthropogenic CH₄ emissions (IPCC, 2021).

The rapid rise in atmospheric CH₄levels, primarily attributed to the agriculture and waste sectors, alongside the fossil fuel sector, underscores the urgent need for robust mitigation measures (Jackson et al., 2020). As the world moves towards net-zero GHG emissions across all sectors, significant reductions in agricultural emissions, particularly non-CO₂ GHGs, are imperative. However, achieving complete elimination of some agricultural emissions remains challenging (IPCC, 2023).

Numerous national and international commitments have been made to achieve net-zero emissions or substantial emission reduction in the various sectors within agriculture. For example, 155 governments worldwide have supported global efforts to reduce methane emissions by 30% by 2030 from 2020 levels (www.globalmethanepledge.org). In the U.S., the dairy and beef industries have set ambitious targets for GHG neutrality, aiming for GHG neutrality by 2050 and climate neutrality by 2040, respectively (Innovation Center for U.S. Dairy, 2022; U.S. Roundtable for Sustainable Beef, 2022). Similarly, Dairy Farmers of Canada have committed to reaching net-zero GHG emissions by 2050. Multinational companies with interest in agriculture have also made various commitments to achieve net-zero by 2050 or earlier. This study primarily focuses on pathways to achieve net-zero emissions in livestock production, using dairy as an example.

Understanding Climate Neutrality or Net-Zero Emissions

The term "climate neutral" is increasingly used, but its lack of a universally agreed-upon definition leads to various interpretations. Generally, it is associated with achieving net-zero GHG emissions (FAO, 2023). The IPCC (2021) specifically defines ‘carbon neutrality’ in terms of CO₂, defining it as a state where human-caused CO₂ emissions are equally counteracted by human-driven CO₂removal efforts. For encompassing all types of GHGs beyond CO₂, the term "GHG neutrality" is used by the IPCC (2021). Climate neutrality may extend beyond GHGs to balance other climate influencers like aerosols or albedo changes (FAO, 2023). Because not all GHG have similar impacts on climate, a global warming potential (GWP) is assigned to each gas relative to CO₂ to provide a common currency in quantifying emissions.

The term ‘climate neutral’ has also been used to describe a system that makes either no net contribution to changes in radiative forcing (Ridoutt, 2021) or no net contribution to additional temperature increases (Costa et al. 2021). This perspective emphasizes managing emissions to stabilize the climate, significantly altering the perceived impact of short-lived gases such as CH₄. When CH₄emissions decrease gradually, their contribution to warming remains stable over time, as quantified using metrics such as GWP*. However, assessing climate neutrality requires considerations beyond physical science, including economic, social, and political factors (FAO, 2023). Different interpretations have various implications for emission reduction efforts, especially concerning short-lived gases. Consequently, without clear definitions, claims and targets of climate neutrality or net-zero emissions can be misunderstood and misinterpreted, leading to ineffective mitigation efforts. For this study, ‘net zero emissions’ refers to achieving net zero GHG emissions using the GWP 100 factor in line with the Paris Agreement.

Pathways to Achieving Net Zero Emissions

Livestock production systems are highly diverse, meaning there is no singular pathway to achieve net-zero emissions. For instance, in low- and middle-income countries, the focus should be on reducing emissions intensity, which involves increasing productivity to lower the emission profile per unit of product. By enhancing productivity and adopting better animal husbandry practices, the California dairy industry has successfully reduced GHG intensity by almost half, aiming to go below 1 kg of CO₂ eq per kg of energy-corrected milk (Naranjo et al., 2020). This study delves into pathways to achieve net zero in high-income intensive production systems, focussing on carbon intensive activities within the livestock industry, including feed production, enteric methane emissions, manure management and fossil fuel use.

Optimizing diet and associated feed production. Matching feed resources with the nutritional requirements of animals helps minimize the GHG burden of livestock products. While many farmers rely on national recommendations or nutritionists to optimize diets, there is still room for improvement. Specialty feed ingredients, such as IntelliBond®, can maximize nutrient utilization by the animal, while others, like proteases, enhance protein digestibility. Lowering the crude protein content in dairy cow diets from approximately 17% to 14% has been identified as a method to decrease the GHG intensity of dairy operations in the United States (Veltman et al., 2021).

Moreover, utilizing byproducts can further lower the overall GHG emissions of livestock products. For example, grape pomace, the residual material left after making wine, can serve as a feed supplement for ruminants. Studies have shown that feeding grape pomace not only improves milk yield but also reduces CH₄emissions by up to 20% and enhances milk quality (Moate et al., 2014). In California, feeding dairy cattle with up to 15% grape pomace has replicated these results, with the added benefit of replacing ingredients with potentially higher GHG emissions.

Livestock consume one third of global cereal production and uses about 40% of global arable land (Mottet et al., 2017). Therefore, practices that reduce emissions per kilogram of crop production also contribute to lowering livestock's share of emissions. These practices include no-till farming, organic amendments, cover crops, crop rotation, and improved nutrient management. Most of the GHGs affected by changes in feed production are N2O and CO₂.

Enteric methane emissions. Over the last 5 to 10 years, there have been considerable advancements in technologies to reduce enteric methane emissions. FAO (2023) has identified over 30 practices that help reduce CH₄emissions, ranging in effectiveness from < 10% to over 90%. Various feed additives are currently in development and hold promise to effectively mitigate emissions. Canada recently approved a feed additive, 3-NOP, that has been shown to consistently reduce emissions by about 30% in dairy cattle (Kebreab et al., 2023). Recent long-term study showed that supplementation with 3-NOP resulted in significant reductions in CH₄emissions (21%-27%) and increased milk yield by up to 6.5%, with its efficacy influenced by diet composition and lactation stage (van Gastelen et al., 2024). Algae containing bromoform have also shown reductions of 50 to 80% in dairy cattle, with one product already receiving generally regarded as safe (GRAS) certification. Other potential solutions include vaccines and microbial engineering to substantially reduce enteric CH₄emissions.

Manure methane emissions.There are several common manure management practices that can reduce CH₄emissions. Anaerobic digestion techniques are the most effective, converting carbon substrates to biogas, which can then be burned or converted to electricity or liquefied gas (EPA, 2024). Other technologies with considerable impact include daily spreading, pasture-based management, composting, solid storage, manure drying practices, semi-permeable covers, natural or induced crusts, decreased manure storage time, compost bedded pack barns, and solid separation of manure solids prior to entry into a wet/anaerobic environment. The effectiveness of these technologies varies but can range from 10 to over 90%. Through the use of anaerobic digesters, California is expected to reduce manure CH₄emissions by 4.2 Mt CO₂e with further 0.6 to 1.1 Mt CO₂e reduction achievable using alternative manure management practices (Kebreab et al., 2022).

Fossil fuel use. Reducing fossil fuel use is also essential. Implementing more energy-efficient solutions for milk processing activities, such as milking and cooling, can result in lower energy usage and subsequent decreases in GHG emissions. These improvements may include enhancements in refrigeration systems, lighting, heating, and various other processing procedures.

Soil carbon sequestration. There are various estimates of carbon uptake capacity in agricultural land by improved management. Estimates suggest that improved management practices could sequester between 2-3 Gt C per year in the top 1m of global agricultural soils, representing 20- 35% of global anthropogenic GHG emissions (Minasny et al., 2017). However, challenges remain, with some suggesting that the actual sequestration potential globally will be in the order of 0.4 to 1.1 Gt C annually (de Vries 2018), because the area where optimized practices can be applied is often overestimated. Nevertheless, even at the lower estimate, soil carbon sequestration can effectively offset emissions, especially considering that some emissions are unavoidable and need to be balanced out. Continued efforts and advancements in these pathways are essential for the livestock sector to achieve net-zero emissions, ensuring environmental sustainability and food security for future generations.

Conclusions

Achieving net-zero emissions in livestock production is a complex but crucial endeavor for mitigating climate change and ensuring the sustainability of our global food system. Through a multifaceted approach that includes optimizing diets, adopting innovative technologies, improving manure management practices, reducing fossil fuel usage, and enhancing soil carbon sequestration, significant progress can be made towards this goal. However, it's essential to recognize that complete elimination of emissions may not be feasible, and thus, a combination of emission reduction strategies and carbon removal techniques will be necessary. Collaboration among stakeholders, ongoing research, and a steadfast commitment to sustainable practices will be paramount in realizing a future where livestock production not only minimizes its environmental impact but also continues to support human nutrition and livelihoods worldwide.

Presented at the 2024 Animal Nutrition Conference of Canada. For information on the next edition, click here.