Current state of enteric methane and the carbon footprint of beef and dairy cattle in the United States

Authors: DILLION, JASMINE - Colorado State University; STACKHOUSE-LAWSON, KIM - Colorado State University; THOMA, GREG - Arkansas State University; Gunter, Stacey; Rotz, Clarence - Al; KEBREAB, ERMIAS - University Of California, Davis; RILEY, DAVID - Texas A&M University; TEDESCHI, LUIS - Texas A&M University; VILLALBA, JUAN - Utah State University; MITLOEHNER, FRANK - University Of California, Davis; HRISTOV, ALEX - Pennsylvania State University; ARCHIBEQUE, SHAWN - Colorado State University; RITTEN, JOHN - University Of Wyoming; MUELLER, NATHAN - Colorado State University

Submitted to: Animal Frontiers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2021
Publication Date: 9/6/2021
Citation: Dillion, J., Stackhouse-Lawson, K., Thoma, G., Gunter, S.A., Rotz, C.A., Kebreab, E., Riley, D.G., Tedeschi, L., Villalba, J., Mitloehner, F., Hristov, A., Archibeque, S., Ritten, J.P., Mueller, N. 2021. Current state of enteric methane and the carbon footprint of beef and dairy cattle in the United States. Animal Frontiers. 11(4):57-68. https://doi.org/10.1093/af/vfab043.
DOI: https://doi.org/10.1093/af/vfab043

Interpretive Summary: Livestock are an integral part of food systems worldwide due to their ability to utilize non-arable land and human-inedible feeds to produce high-quality, human-edible protein in the forms of meat and milk, with byproducts used in fertilizer, textiles, soaps, and a host of other societally beneficial products. These benefits are in contrast to impacts on the environment, which are projected to increase with an increasing population and demand for nutritiously dense foods. Agriculture contributes about a sizable amount of the US's greenhouse gas emissions. Hence, livestock directly contributes about half of the US's total agriculture. Livestock contribute directly and indirectly by way of land and water use through grazingland and also cropland that produce feed. Significant progress has been made in measuring, monitoring, and modeling greenhouse gas emissions from livestock production, though uncertainties in actual amounts still exist. As experimental capabilities improved, so have the use of mathematical models used to inform experimental hypotheses and extrapolate experimental results to predict the implications of interventions. These models range from empirical and mechanistic representations of animal nutrition to whole farm system modeling and life-cycle assessment of the full supply chain. More recently is research investigating the co-benefits of grazing diverse landscapes on livestock’s environmental impacts; genetic improvement for improved productivity through improved animal fitness traits; and the exploration of soil carbon sequestration as potential greenhouse gas mitigator for agricultural systems. Thrust into the public eye in recent years has been the exploration of soil carbon sequestration as a natural climate solution, though the approach is not without its uncertainties and criticisms. Most recently, there has been an increases in the advancement of technological and management interventions for reducing environmental impacts of livestock production systems, even with considerable uncertainty and heterogeneity in results across ecosystems. While understanding the dynamics of individual animals or herds is integral to understanding and decision making for livestock sustainability research, it must be scaled up to integrate other disciplines including a broad sustainability framework. To provide holistic representation of sustainability research results, and to explore the significant role that people, policy, and economics play in farm decision making and associated sustainability outcomes. To conduct sustainability work, animal science researchers should collaborate with interdisciplinary teams to include actors throughout the supply chain including those with traditional and practical knowledge.

Technical Abstract: Livestock are an integral part of food systems worldwide due to their ability to utilize non-arable land and human-inedible feeds to produce high-quality, human-edible protein in the forms of meat and milk, with byproducts used in fertilizer, textiles, soaps, and a host of other societally beneficial products. These benefits are in contrast to impacts on the environment, which are projected to increase with an increasing population and demand for nutritiously dense foods. Agriculture contributes about 8 to 10% of U.S. greenhouse gas emissions. Livestock directly contributes about half of the U.S. agricultural total, including animal, manure, and field-associated emissions. Of these, beef represent about 3% while dairy represents about 1.5%. Livestock contribute directly and indirectly to land occupation and water use through grazingland and cropland used to produce feed crops. Significant progress has been made in measuring, monitoring, and modeling greenhouse gas emissions from livestock and manure, though uncertainties still exist. As experimental capabilities improved, so, to have mathematical models used to inform experimental hypotheses and extrapolate experimental results to predict the implications of interventions at the animal scale on the sustainability of livestock production systems. These models range from empirical to mechanistic representation of animal nutrition to whole farm system modeling and life-cycle assessment of the full supply chains. Significant progress has also been made understanding methods for nutrition, pen, grazing, and crop management interventions to control nutrient losses that contribute to negatively impact air and water quality. More nascent is research investigating the co-benefits of grazing diverse landscapes on livestock’s environmental impacts; genetic improvement for improved productivity through improved animal fitness traits; and the exploration of soil carbon sequestration as potential greenhouse gas mitigator for agricultural systems. Catapulted into the public eye in recent years, exploration of soil carbon sequestration as a natural climate solution has gained significant attention, though the approach is not without its uncertainties and criticisms. Most recently, there has been an increase in the advancement of technological and management interventions for reducing environmental impacts of livestock production systems—even with considerable uncertainty and heterogeneity in results across ecoregions. While understanding the dynamics of individual animals or herds is integral to understanding and decision making for livestock sustainability research that must be scaled up to integrate other disciplines including a broad sustainability framework. To provide holistic representation of sustainability research results, and to explore the significant role that people, policy, and economics play in farm decision making and associated sustainability outcomes. To conduct sustainability work, animal science researchers should collaborate with interdisciplinary teams to include actors throughout the supply chain including those with traditional and practical knowledge to (1) imbed livestock sustainability research in food production systems or sustainable development goal frameworks; (2) clearly define the context and underlying frameworks within which the research is grounded; and (3) use mixed methods within frameworks to explore environmental, social, and economic aspects of sustainability problems and proposed solutions.