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In the U.S., agriculture is responsible for 9.4% of total greenhouse gas (GHG) emissions (EPA, 2023). That same report states that in 2021, methane produced from enteric fermentation in the U.S. accounted for 194.9 million metric tons (MMT) of carbon dioxide equivalent (CO2EQ.). This represents 3.1% of the total U.S. emissions, or 33% of total agricultural emissions.

However, given the size of the livestock sector, in 2021, methane produced from enteric fermentation in the U.S. was equivalent to 66% of the total GHG of Spain. When contrasting the contribution of this important segment of the U.S. economy with the total GHG emissions of an industrialized country like Spain, which in addition has a sizeable agricultural industry, it becomes evident that there is an imperative need to address enteric methane emissions domestically to contribute globally to one of the greatest challenges of all times: sustainable food production for an ever-growing population.

As we move toward the next couple of decades, the world's agriculture will face one of the greatest challenges of all time: to produce enough food to feed the 9 billion people the Earth will hold by 2050. Without question, this will demand the concerted efforts of producers, researchers, and policymakers to provide the experience, technology, and legal framework necessary to accomplish such a difficult endeavor.

Among the different sources of animal protein, beef is the most nutrient dense on a per calorie basis, supplying several of the essential vitamins and minerals with a relatively low caloric intake per serving. Ruminants such as cattle, sheep, and goats have a unique advantage over non-ruminants in terms of nutritional physiology, because they carry microorganisms in their gastrointestinal tract (GIT) that hold the key to the digestion of fiber.

Fiber is present in forages in the form of cellulose and is the most abundant complex carbohydrate on Earth. By harboring microorganisms in their GIT, ruminants can take advantage of fiber digestion by creating a symbiotic relationship between the microbes and the ruminant host. The microbes digest the fiber and produce by-products known as volatile fatty acids, which are in turn used by the ruminant animal as an energy source. In return, the ruminant host provides a good environment for the microorganisms and plenty of feed to sustain their growth.

For this reason, cattle, sheep, and goats can thrive in environments where no other type of production system can take place. Unfortunately, this advantage by ruminants in terms of their ability to digest fiber comes at a cost. The production of greenhouse gases such as carbon dioxide and methane is a result of the enteric fermentation of feedstuffs, and those greenhouse gases are released by cattle as a necessary byproduct of their fermentation of fibrous feeds.

The greenhouse effect of certain gases refers to their ability to trap the heat that is generated when the sun radiation bounces back after hitting the Earth's surface. That radiation cannot escape, and thus increases the atmospheric temperature, affecting biological processes in diverse manners. Those gases with such capacity to retain heat are called greenhouse gases (GHG), and the three most common gases are carbon dioxide, methane, and nitrous oxide.

The ability to produce methane, the main contributor of the GHG emitted by cattle, is much greater in animals consuming forage than those consuming a high-grain diet. Thus, segments of beef production chain that involve the use of forages as the main resource are greater contributors in terms of GHG emissions. Beef and dairy cattle, swine, horses and small ruminants are all contributors to the 194.9 MMT of CO2EQ. produced via enteric fermentation in the U.S. However, beef cattle are the greatest contributors by far, with 71% of total enteric methane, distantly followed by dairy cattle which contribute with 25% of those emissions (EPA, 2023).

Based on these statistics, research efforts to mitigate enteric methane emissions should begin to focus more on beef production systems, and particularly those segments of the industry in which forages play a large role (e.g., cow-calf, stocker, etc.). Currently available strategies to mitigate methane are very few, and most of them are facing regulatory challenges because of the nature of their production (e.g., synthetic molecules) or because of potential toxicity (e.g., macroalgae feeding).

The two most promising feed additives for enteric methane mitigation in the U.S. are either not approved as of yet, or may pose additional challenges in terms of food safety or environmental impact. It is quite concerning that the future sustainability of animal production systems in terms of carbon footprint, relies on such few tools, and almost none with the potential for immediate widespread use and impact.

To guarantee the long-term sustainability of livestock systems in the U.S., action needs to be taken immediately to promote the development of a greater portfolio of feed additives with potential to decrease methane emissions. This project is poised to our long-term goal is to reduce the enteric CH4 emissions in the U.S. livestock industry with concomitant improvements in the sustainability of cow-calf and stocking systems.

Our overall objective is to develop the next generation of safe, efficacious, and affordable feed additives to mitigate enteric methane emissions in ruminants. We are particularly well prepared to conduct the proposed research due to our unique access to multiple research herds and facilities to simultaneously conduct the multiple studies required to meet our objectives. In addition, we have assembled a team that combines ruminant nutritionists, forage agronomists, chemists, biochemists, microbiologists, and extension state specialists, each of whom has vast expertise and publications records in the different areas of this project.

Thus, the available resources and complementary expertise of our group are especially conducive to the successful completion of the proposed investigations. We plan to accomplish our overall objective for this project by pursuing the following four supporting objectives: Objective 1: Production and purification of immunogens and 2-hydroxyethylphosphonate (HEP) Objective 2: Optimization of the dose and impact on microbiome and digestibility Objective 3: Deployment and delivery of new additives Objective 4: Extension and outreach to assess adoption rate and impact on stakeholders.

The expected results from this study are that these additives may contribute to a reduction of a minimum of 25% in U.S. enteric methane emissions, which would amount to 48 million metric tons of carbon dioxide equivalent per year. Put in context, these emissions reductions are equivalent to the total emissions produced by the state of Nebraska in one year, including all the different segments of the state's economy (energy, transportation, agriculture, etc.).

The anticipated impact of this project is the ability to maintain the current levels of animal protein production that have made the U.S. agriculture so competitive over the years, while reducing significantly the emissions associated with it. The world is currently desperately searching for alternatives to decrease the carbon footprint of food production. The development of affordable and ready-to-use additives for the livestock industry with the potential to decrease enteric methane will position the U.S. as a leader in climate-smart agriculture, while providing its producers with a competitive advantage in terms of technology.

University Of Florida

10.310 - Agriculture and Food Research Initiative (AFRI)

Institute of Bioenergy, Climate, and Environment (IBCE) [USDA - NIFA]

Gainesville, Florida 32611-1941 United States

Single Zip Code

Agriculture and Food Research Initiative Sustainable Agricultural Systems (USDA-NIFA-AFRI-009802)