Emissions by source

Emissions from livestock supply chains originate from four main processes: enteric fermentation, manure management, feed production and energy consumption. GLEAM provides disaggregated information on emissions from those pathways.

Enteric fermentation accounts for the methane generated during the digestive process of ruminants -although non-ruminants species also produce methane when digesting, the amount is much lower. Feed quality is closely correlated with enteric emissions. Poorly digestible rations, i.e. highly fibrous ingredients, yield higher enteric methane emissions.

Manure acts as a source of both methane and nitrous oxide. Methane is released during anaerobic decomposition of organic matter. Nitrous oxide is mainly generated during manure ammonia decomposition. Different manure management systems (MMS) can lead to different emission levels. In general terms, methane emissions are higher when manure is stored and treated in liquid systems (lagoons or ponds), while dry MMS such as drylot or solid systems tend to favor nitrous oxide emissions.

There are several emissions related to feed production. Carbon dioxide emissions arise from expansion of feed crops and pastures into natural areas such as forests, from manufacture of fertilizers and pesticides for feed crops and from feed transportation and processing. Nitrous oxide emissions are caused by the use of nitrogenous fertilizers and by direct application of manure both in pastures and crop fields.

Energy consumption occurs along the entire supply chain. Production of fertilizers and the use of machinery for crop management, harvesting, processing and transport of feed crops generate GHG emissions, which were accounted as part of the emissions from feed production. Energy is also consumed on animal production site for ventilation, illumination, milking, cooling, etc. Finally, livestock commodities are processed, packed and transported to retail points, which involves further energy use.

Enteric fermentation accounts for 44 percent of total sector's emissions, with about 3.5 gigatonnes CO 2 -eq. Feed production is the second largest source of emissions, with 3.3 gigatonnes CO 2 -eq or about 41 percent of total emissions. Manure management is responsible for almost 10 percent of the total, or 0.8 gigatonnes CO 2 -eq. Energy consumption, both on-farm and postfarm, account for 0.4 gigatonnes CO 2 -eq, or nearly 5 percent of the total.

Global emissions by source. Relative contribution of main sources of emissions from global livestock supply chains.

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