Fifty years of environmental progress for United States dairy farms

Authors: Rotz, Clarence - Al; BEEGLE, DOUG - Pennsylvania State University; BERNARD, JOHN - University Of Georgia; Leytem, April; Feyereisen, Gary; HAGEVOORT, ROBERT - New Mexico State University; HARRISON, JOE - Washington State University; AKSLAND, GENE - Consultant; THOMA, GREG - Colorado State University

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/5/2023
Publication Date: 1/10/2024
Citation: Rotz, C.A., Beegle, D., Bernard, J.K., Leytem, A.B., Feyereisen, G.W., Hagevoort, R., Harrison, J., Aksland, G., Thoma, G. 2024. Fifty years of environmental progress for United States dairy farms. Journal of Dairy Science. 107(6):3651-3668. https://doi.org/10.3168/jds.2023-24185.
DOI: https://doi.org/10.3168/jds.2023-24185

Interpretive Summary: Many changes have occurred in the technology, management, and the resulting performance of United States dairy farms over the past 50 years. Efficiency in milk production has increased greatly with about 20% fewer cows producing about twice the milk today. Other improvements include increased crop yields for feed production, more efficient fuel use, and improved efficiency and reduced energy use in the production of many farm inputs such as fuel, electricity, and fertilizers. Across all environmental categories, intensities expressed per unit of milk produced have decreased substantially over this period but totals over all milk produced show increases in emissions of ammonia, methane, and other volatile organic compounds. Life cycle greenhouse gas emissions have increased 13% with little change in fossil energy use. Emissions of ammonia, methane, and volatile organic compounds have increased while nutrient losses to ground and surface waters have decreased. Expansion in the dry climate of the west has contributed to a 40% increase in water use, perhaps the greatest threat to future sustainability of dairy farms. Although much progress has been made in improving production efficiency and reducing or controlling environmental impacts, further mitigation is needed to continue improving the sustainability of the dairy industry.

Technical Abstract: Dairy farm management in the United States has changed in many ways over the past 50 years. Efficiency in milk production has increased greatly with about 20% fewer cows producing about twice the milk today. Other improvements include increased crop yields, improved fuel efficiency of farm equipment and improved efficiency in producing most resources (electricity, fuel, fertilizer, etc.) used on farms. These improvements have led to many changes in the environmental impact of farms. Through simulation of representative dairy farms in 1971 and 2020, changes at the farm-gate in nutrient losses and life cycle assessments of greenhouse gas (GHG) emissions, fossil energy use, and non-precipitation (blue) water use were determined for six regions of the U.S. and the full nation. For all environmental metrics considered, reductions were found for the intensity expressed per unit of fat and protein corrected milk produced, but the impacts over all farms and milk produced sometimes increased. Reductions in the impacts of dairy farms in the eastern U.S. were offset by large increases in western regions because of a major increase in cow numbers in the west. The national average intensity of GHG emissions decreased by 42%, which gave just a 14% increase in the total GHG emission of all dairy farms over the 50-year period. The intensity of fossil energy use decreased by 54% with the total for all farms decreasing 8%. Water consumption related to dairy farm production decreased in intensity by 29%, but due to the large increase in dairy production in the dry western regions with greater dependence on irrigated feed crops, total blue water use increased 40%. Major pathways of nitrogen loss included ammonia volatilization, leaching, and denitrification, where total ammonia emissions related to U.S. dairy farms increased 27% while leaching losses decreased by 36% with little change in nitrous oxide emission. Simulated nitrogen and phosphorus runoff losses from all dairy farms decreased 27 to 51% through more efficient fertilizer use, reduced tillage, and greater use of cover crops. Emissions of methane and reactive non-methane volatile organic compounds increased 31% and 50%, respectively, due to greater use of long-term manure storage and silage storage in bunkers and piles. Reductions in environmental intensities reflect the progress made in improving the efficiency of U.S. dairy farms and this has reduced the total impact of all dairy farms for many environmental metrics. Although progress has been made in many areas, improved production strategies are needed for continued growth in milk production and the mitigation of emissions, particularly in view of projected climate variability.