The purpose of this project is to review the current understanding of methodologies available for the mitigation of Greenhouse gas emissions from livestock production. Greenhouse gas emissions from livestock production are largely associated with naturally occurring biological processes in the animal and particularly within the symbiotic microorganisms associated with these animals and their excreted waste products. Enteric emissions are primarily a result of CH4 producing microorganisms, called methanogens that exist in the gastrointestinal tract of most animals. However the quantity produced by these methanogens is dependent on the development of the gastrointestinal tract of the animal that they are associated with. For example, ruminants produce a much greater quantity of methane because of the presence and fermentative capacity of the rumen that monogastrics, such as swine, do not have. Although non-ruminant species can also produce methane via hindgut fermentation, the quantities of methane associated with hindgut fermentation are much less than that of foregut fermenters, such as ruminants. To clarify, in 2009, enteric fermentation contributed 71% of CH4 from agriculture (6,655 Gg of 9,372 Gg CH4), and ruminants were responsible for 96% (6,385 Gg), horses 2.5% (171 Gg) and swine 1.5% (99Gg) of the enteric emissions in the US(EPA, 2009). Additionally, livestock manure can emit CH4 and N2O during storage and with field application. Storage conditions (aeration, temperature, pH) as well as manure composition have a major influence on the gases emitted and rates of emission. Methane emissions from manure that is stored can be reduced by cooling, covering, separating solids from slurry, or by capturing the CH4 emitted.
What did we do
We conducted a thorough review of the existing literature regarding GHG emissions from livestock in the U.S.
What have we learned
We have learned that there are myriad opportunities to reduce GHG emissions from livestock. Additionally, many of the practices that will reduce GHG emissions will also tend to concomitantly increase the efficiency of production of the livestock and their products. Unfortunately, there are limited amounts of data on the potential unintended side effects also associated with the push for improved efficiencies from livestock production. While some practices may target specific modes of GHG emissions, most are focused on improving the overall efficiency of production.
We are currently working to expand our research capabilities to evaluate future mitigation techniques and continue to work with EPA and USDA on numerous public projects to enhance producer mitigation of GHG emissions.
A thorough review (Carbon Sequestration and Greenhouse Gas Fluxes in Agriculture: Challenges and Opportunities) of the issues discussed here and in agriculture in general is available at the Council for Agricultural Science and Technology website ( http://www.cast-science.org/publications/?carbon_sequestration_and_greenhouse_gas_fluxes_in_agriculture_challenges_and_opportunities&show=product&productID=27392 )
Shawn Archibeque, Colorado State University
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