Production of milk causes environmental side effects, such as emission of greenhouse gases and nutrient enrichment in surface water. Scientific evidence that shows differences in integral environmental impact between milk production systems in the Netherlands was underexposed. In this paper, two Dutch milk production systems, i.e. a conventional and an organic, were compared on their integral environmental impact and hotspots were identified in the conventional and organic milk production chains. Identification of a hotspot provides insight into mitigation options for conventional and organic milk production. Data of commercial farms that participated in two pilot-studies were used and refer to the year 2003. For each farm, a detailed cradle-to-farm-gate life cycle assessment, including on and off farm pollution was performed. Results showed better environmental performance concerning energy use and eutrophication potential per kilogram of milk for organic farms than for conventional farms. Furthermore, higher on-farm acidification potential and global warming potential per kilogram organic milk implies that higher ammonia, methane, and nitrous oxide emissions occur on farm per kilogram organic milk than for conventional milk. Total acidification potential and global warming potential per kilogram milk did not differ between the selected conventional and organic farms. In addition, results showed lower land use per kilogram conventional milk compared with organic milk. In the selected conventional farms, purchased concentrates was found to be the hotspot in off farm and total impact for all impact categories, whereas in the selected organic farms, both purchased concentrates and roughage were found to be the hotspots in off farm impact.
"We recommend to improve integral environmental performance of milk production by: (1) reducing the use of concentrates ingredients with a high environmental impact, (2) decreasing the use of concentrates per kilogram of milk, and (3) reducing nutrient surpluses by improving farm nutrient flows.