An environmental assessment of grass-based dairy production

Authors: Rotz, Clarence - Al; HOLLY, MICHAEL - University Of Wisconsin; DE LONG, ARRON - Consultant; EGAN, FRANKLIN - Consultant; Kleinman, Peter

Submitted to: Applied Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2020
Publication Date: 9/1/2020
Publication URL: https://handle.nal.usda.gov/10113/6985769
Citation: Rotz, C.A., Holly, M., De Long, A., Egan, F., Kleinman, P.J. 2020. An environmental assessment of grass-based dairy production. Applied Animal Science. 184:1-9. https://doi.org/10.1016/j.agsy.2020.102887.
DOI: https://doi.org/10.1016/j.agsy.2020.102887

Interpretive Summary: The market for milk produced by cows on a predominately-grass or all-grass diet has increased rapidly in recent years due to reported human health benefits of the milk and perceived environmental and animal welfare benefits. Our objective was to quantify important environmental aspects of grass-based dairy farms in Pennsylvania, including nitrogen and phosphorus losses and life cycle assessments of water use, fossil energy use, reactive nitrogen loss and greenhouse gas emissions. Comparisons were made of production systems using all-grass, grass supplemented with grain feeding, traditional feeding in confinement, and an average of all Pennsylvania dairy farms. Grass-based dairy farms can provide environmental benefits to a watershed by reducing losses from farmland. Due to the relatively low milk production per cow though, they have a disadvantage from a global perspective of providing milk with the least impact on the environment per unit of food produced.

Technical Abstract: We compared all-grass, grass supplemented with grain, and full confinement dairy production systems using a whole-farm model and found that for many environmental sustainability indicators, the grass-based systems had smaller environmental impacts per unit of farmland but larger impacts per unit of milk produced compared to confinement fed systems. Grass-based dairy production, which relies heavily on grazing and use of forage crops, is growing primarily due to reported human health benefits of the milk produced and perceived environmental and animal welfare benefits. Data and information on production practices were gathered from eight dairy farms in Pennsylvania. Four of the farms grazed and fed only forage, and four supplemented the forage with some grain. From the information obtained, each farm was simulated with the Integrated Farm System Model to verify proper representation of their production practices. Due to variation in climate, soil characteristics and management practices, a comparison of the two grass-based farm types showed no significant differences in environmental impacts. Farms of the same size using each production strategy along with a more traditional confinement fed production system were then simulated using the same climate and soil conditions for a better comparison. Predicted nitrogen and phosphorus losses to the environment, fossil energy use, water use, and greenhouse gas emissions were less from the grass-based farms compared to the confinement operation. Due to lower milk production on the grass-based dairy farms, nutrient losses and greenhouse gas emissions expressed per unit of milk produced were generally greater than those of the confinement system. Within the grass-based dairy systems, the system that supplemented with grain had slightly lower nitrogen and phosphorus losses per unit of farmland compared to the grass-only system, and much lower losses and emissions when expressed per unit of milk produced. Total production cost was less for the all-grass dairy than the grass with grain dairy. With a greater milk price, the all-grass system provided greater profitability per unit of land used and per unit of milk produced compared to the other production systems. These data indicate that grass-based dairy farms can provide environmental benefits to a local watershed, but due to a lower efficiency in milk production, they may increase the aggregate environmental impacts of regional and global supply chains.