Appraisal of environmental profiles of pasture-based milk production: a case study of the Waikato region, New Zealand

Purpose: Dairying is a relatively intensive livestock production system and contributes to environmental impacts. In the southern hemisphere, dairy farming systems are based mainly on outdoor grazing of permanent pastures. Multiple environmental impacts associated with this system have not been quantified. The purpose of this study was to (i) assess environmental profiles and (ii) identify environmental hotspots in a pasture-based dairy farming system. Methods: A life cycle assessment of 53 individual dairy farms in the Waikato region, New Zealand was carried out, using one kg of fat and protein corrected milk as a functional unit and the cradle-to-farm gate as a system boundary. Twelve environmental impact categories were assessed. The impact categories assessed included Climate Change (CC), Ozone Depletion Potential (ODP), Cancer effects (Cancer), Non-cancer effects (Non-cancer), Particulate Matter (PM), Ionizing Radiation (IR), Photochemical Ozone Formation Potential (POFP), Acidification Potential (AP), Terrestrial Eutrophication Potential (TEP), Freshwater Eutrophication Potential (FEP), Marine Eutrophication Potential (MEP) and Ecotoxicity for Aquatic Freshwater (Ecotox). Contribution and sensitivity analyses were performed to determine key hotspots for each impact category. Results and discussion: The on-farm stage contributed 37-73% of the total impacts for all environmental indicators except for IR and Ecotox where manufacturing of agrichemicals (i.e. chemical fertilizers and pesticides) for use on the dairy farms played a dominant role. The rearing of replacement animals grazed off-farm and the associated land contributed 11-20% to the total impacts for all environmental indicators. Of the total impacts, the production of brought-in feeds for use on the dairy farms played a role in the impacts on Non-cancer (25% of the total impacts), FEP (15%), MEP (12%) and Ecotox (19%). The manufacturing of agrichemicals contributed largely to the impacts on ODP (26%), Cancer (26%), PM (19%), IR (46%), FEP (25%) and Ecotox (42%). The stage of transportation of off-farm inputs, for use on the dairy farms, contributed to the impacts on ODP (15%), IR (21%) and POFP (11%). Sensitivity analysis demonstrated the markedly important contribution of different data sources, inventory models and choice of impact assessment methods to the results. Conclusions: Pasture-based dairy farming systems contributed to a range of environmental impacts and the on-farm stage dominated the results for most environmental indicators. The rearing of replacement animals, the use of brought-in feeds, the manufacturing of agrichemicals and transportation of off-farm inputs for using on dairy farms played a significant role in different environmental indicators