The importance of livestock in global and national GHG emissions
In 2010, agriculture emitted about 5.4 Gt CO2e, accounting for about 11% of global GHG emissions (Tubiello et al. 2015). Of total agricultural emissions, about 60% is due to livestock emission sources, with enteric fermentation contributing ~63% of livestock emissions, manure management contributing ~12% and deposit of dung and urine on pasture contributing ~25% of livestock emissions. Data from FAO for 185 Parties to the UNFCCC suggests that the main livestock emission sources account for about 16.5% of their total GHG emissions, but exceed 10% of total GHG emissions in 78 countries (i.e. 42% of 185 countries) (FAOSTAT).
In addition to these direct livestock emission sources, further livestock-related emissions occur in feed production and processing and land use change driven by demand for animal feed, as well as in livestock product transport and processing. When these emissions are included, livestock contribute about 14.5% of global anthropogenic emissions, most of which is due to dairy and beef cattle production (Gerber et al. 2013).
Globally, livestock GHG emissions have been contributing an increasing share of agricultural emissions over time (Tubiello et al. 2015). While total GHG emissions from livestock production in developed countries as a whole have declined in recent decades, emissions from cattle, pigs and small ruminants in developing countries have increased significantly (Caro et al. 2014). Further growth in production and consumption of livestock products is projected in developing countries in the coming decades, with the highest increase in total and per capita consumption projected to occur in low- and lower-middle income countries (Robinson & Pozzi, 2011). Although some increase in demand will be met by trade with developed countries, GHG emissions from livestock production in developing countries can be expected to continue to increase.
Despite the increase in total emissions from livestock production in developing countries, GHG emission intensity (tCO2e per tonne of livestock product) has been decreasing (Caro et al. 2014). Increases in the efficiency of livestock production whether through transformation of livestock production systems or through productivity and efficiency improvements within production systems are therefore an important way to meet increasing demand for livestock products while limiting impact on the global climate system (Gerber et al. 2013, Havlík et al. 2014). The livestock sector accounts for up to half the technical mitigation potential in agriculture, forestry and land use, and the majority of livestock mitigation options are either costless to producers or have low costs (Herrero et al. 2016; Henderson et al. 2017).
Guidelines from the Intergovernmental Panel on Climate Change (IPCC) for national GHG inventory compilation and reporting provide several methodological options for estimating livestock GHG emissions (IPCC 1996, 2000, 2006). Tier 1 methodologies use fixed values for GHG emissions per head of livestock, so changes in total emissions can reflect only changes in livestock populations. Tier 2 methodologies, which require more detailed information on the characteristics and performance of different sub-categories of livestock, are able to better reflect actual production conditions. The global estimates of livestock sector emissions cited above were made using the Tier 1 approach. But measuring the effects of changes in livestock management practices on GHG emissions at the country level requires adoption of a Tier 2 approach that can capture the effects of changes in management and animal performance on GHG emissions. Better characterization of livestock GHG emissions can also assist policy makers to target and design efforts to mitigate GHG emissions in the livestock sector (Wilkes et al. 2017). Given the significance of enteric fermentation emissions and emissions from cattle in many countries’ livestock inventories, applying a Tier 2 approach to estimating enteric fermentation emissions is particularly relevant.
Opportunities to mitigate emissions
Mitigation options that can be implemented now
Improved animal feeding and nutrition. In beef production systems based on poor-quality feeds (such as straw or crop residues) or grazing animals on low-quality pasture, improving feed quality improves productivity and reduces GHG emissions per unit of product. This can be achieved by substituting coarse straws from millet, sorghum or maize for slender straws from rice or wheat or adding maize or legume silages to the diet. In grass-based systems, rotational grazing or changing forage species can improve diet quality. In systems where productivity is already high, precision feeding can maximize feed efficiency and animal productivity (Andeweg and Reisinger, 2014).
Use of efficient animal breeds. Breeding can increase feed efficiency, disease resistance, and weight gain, all of which lead to greater productivity and lower emission intensity.
Good animal husbandry. Sound management of cattle herds maximizes the productive portion of the animal’s life cycle. Specific measures include improved conception rates, earlier time of first reproduction, and reducing time to slaughter. Prevention and early treatment of disease is also key to maximizing productivity.
Avoid land use change. Expansion of pasture or feed crops into forested areas should be avoided. A combination of incentives for investing in intensive, sustainable production systems and public policy that protects forest boundaries has shown initial success in the Brazilian Amazon (Nepstad et al. 2014).
Manage manure to reduce emissions. In grass-based systems, options to reduce nitrous oxide emissions from manure deposited on pasture are limited. However, there are a number of well-tested options to reduce methane and nitrous oxide emissions from storage, transport and disposal of manure from confined animals. Animal housing and manure storage facilities should be designed to prevent runoff into the environment, for example by using concrete or hard clay floors. Aeration of solid and liquid manure can reduce methane emissions. When applying manure back to pasture or feed crops, application rates should be matched to the nitrogen needs of the crop. Finally, anaerobic digesters allow methane to be captured and used as an energy source.
Pasture management. Practices such as improved grazing management, fertilization, sowing of legumes or improved grass species, and irrigation can improve the productivity of pastures as well as potentially increase soil carbon stocks, especially where existing pasture has been degraded (Conant et al. 2017). Silvopastoral systems (in which trees are added to pastures) also have soil potential to sequester carbon in trees and soils (Feliciano et al. 2018).
Potential options requiring further research and development
Many of the currently available strategies to mitigate emissions from beef value chains rely on increasing productivity in order to reduce emission intensity. However, there are also technologies in the pipeline that can reduce emissions from enteric fermentation or fertilizers on an absolute basis.
Rumen modification. Many researchers are currently developing and evaluating strategies to alter the microbial ecosystem in the stomach of ruminant livestock to reduce the production of methane. The basis of these strategies is the inhibition of methanogens—methane-producing microorganisms—relative to other microbes present in the stomach, or other alterations to ruminant digestion that improve feed efficiency. This approach is called rumen modification.
There are several different types of compounds that have been shown to suppress methane production when fed to ruminants that differ in effectiveness, environmental safety, and effects on animal health. The most promising types of feed additives are those that provide nutritional advantages in addition to reducing methane. For example, adding fats or fatty acids (such as oilseeds) to animal diets has the potential to reduce methane while increasing productivity. Nitrates can reduce methane while providing a nitrogen source for animals fed a low-protein diet (Olijhoek et al. 2016). Ionophores are antibiotic compounds that increase feed efficiency and have a moderate effect on methane production (Hristov et al. 2013). Their use is banned in the European Union due to concerns about antibiotic resistant bacteria. However, garlic may have similar effects (Gholipour et al. 2016; Patra, 2016). Certain types of seaweed and algae, long used as feed supplements for their nutritional value, also contain compounds (such as lipids and tannins) that can inhibit methane production in the rumen (Maia et al. 2016).
In addition to feed additives, there are also efforts to develop vaccines that stimulate the animal to produce antibodies against methanogens without reducing productivity (Andeweg and Reisinger, 2014).
Breeding for low methane ruminants. Breeding can increase productivity and reduce emission intensity, but it is also possible to breed animals with low methane production as a selection objective. Breeding for reduced methane is more advanced in sheep, but has potential for cattle as well (de Haas et al. 2016).
Biological nitrification inhibition. Biological nitrification inhibition (BNI) is the natural ability of certain plant species to naturally release chemical compounds from their roots that suppress the activity of soil microbes that convert nitrogen to nitrite and nitrate—a process called nitrification. Once in the form of nitrate, nitrogen is more easily lost as nitrous oxide. BNI can therefore reduce nitrous oxide emissions from pastures and crops (Subbarao et al. 2013). The BNI function is relatively strong in tropical pasture grasses of the genus Brachiaria and in some feed grain crops such as sorghum. Brachiaria grasses, widely planted as forage crops in the tropics, have been shown to reduce N2O emissions (from fertilizer and cattle urine patches) and improve nitrogen retention and recovery in soils (Byrnes et al. 2017; Subbarao et al., 2017). They can improve nutrient use efficiency of maize in crop rotations (Subbarao et al. 2017). Further research is necessary to fully take advantage of this technology, for example by breeding the trait into other food and forage crops.
Livestock NAMAs in preparation or implementation
Several countries are in the process of preparing or implementing NAMAs in the livestock sector.
Brazil is seeking support for implementation of its Beef Supply Chain Resource Efficiency Programme. The design of the MRV system combines a geospatially explicit national agricultural GHG monitoring platform with an app (called AgroTag) that enables submission of standardized data by beef farms.
Colombia is preparing its Sustainable Bovine Livestock NAMA. The country is in the process of developing a data management system to harmonize the bottom-up approaches used by projects and the top-down approaches used in preparation of national inventories
Guatemala is seeking support for preparation of a Sustainable and Low Carbon Bovine Livestock Development NAMA. The MRV system for this NAMA is under development.
Costa Rica is developing a livestock NAMA as one of several mechanisms to implement its National Strategy for Low-Carbon Livestock. The country is developing an integrated monitoring and evaluation infrastructure to support decision-making and reporting for its decarbonization plan, National Adaptation Plan, and NAMAs in the coffee and livestock sectors. Costa Rica already has a National Environmental Information System (SINIA) and is now integrating a National Metrics System for Climate Change (SINAMECC) within SINIA. The NAMA pilot developed a number of indicators to monitor productivity, profitability, and resilience along with changes in GHG emissions on pilot farms.