The livestock sector, especially dairy cattle production, has a major impact on the environment. Environmental impacts vary among dairy cattle production systems. Understanding these differences is important to mitigate impacts of future dairy systems. The aim of this study was to compare environmental impacts of milk produced in contrasting systems based on a literature review of life cycle assessment studies.
We reviewed 14 studies based on four criteria: the main output of a production system under study was milk, the production system under study was situated in an organization for Economic Cooperation and Development (OECD) country, the study included at least all processes from cradle-to-farm-gate, and the study compared at least two contrasting dairy production systems. We classified the studied systems based on the production methods (conventional or organic), and type of diet (concentrate-based or grass-based).
This review resulted higher global warming potential (on average 10% higher), acidification potential (5% higher), eutrophication potential (37% higher), energy use (67% higher), and lower land use (31% lower) per unit of milk for conventional compared with organic systems. The higher impacts in case of conventional systems were explained mainly by a higher use of mineral nitrogen fertilization and a higher use of processed feeds. Furthermore, results showed a higher global warming potential (on average 26% higher), acidification potential (78% higher), eutrophication potential (35% higher), energy use (179% higher), and a lower land use (6% lower) per unit of milk for concentrate-based compared with grass-based systems. The higher impacts in case of concentrate-based systems were also explained mainly by a higher use of mineral nitrogen fertilization and a higher use of processed feeds.
Except for global warming potential, results should be interpreted with care because impacts were compared in a few studies only. Moreover, studies included in this research did not assess all environmental impacts categories, for example, water use, biodiversity loss, and human and eco-toxicity were not or only in a few studies included. Methodological choices, such as choices on how to account for emissions from land use changes, can lead to differences in LCA results. Therefore, further harmonization of LCA methodology can improve comparison of LCA results.
Student: J Nshokeyinka
Supervisor: dr ir C van Middelaar