How methods to assess land-use changes influence the resulting global warming potential and cost of optimized diets: a case study on Danish pigs applying life cycle assessment methodology

Journal article, 2024

Purpose: Meeting the demands of a growing and increasingly affluent population necessitates a deeper understanding of the environmental and economic implications of production. This implication is most relevant in key production sectors including agriculture and livestock. This article is intended to provide an understanding of the influence of methods of assessing land-use change (LUC) with respect to minimizing both the global warming potential (GWP) and the monetary costs of pig feed formulation. Methods: Feed mixtures intended for slaughter pigs were generated for minimal cost and GWP impacts by applying four differing LUC assessment methods. The objective function was the Danish slaughter pig feed unit, minimized for cost in Danish crowns (DKK), with GWP impacts constrained in multiple steps. Attributional LCA methodology was applied using the Agri-footprint 6.3 database, with GWP impacts calculated excluding land use changes, including direct land-use changes and including the carbon opportunity cost. Analyses of the functional relationship between the optimal cost and the GWP impact were conducted, followed by a comparative LCA of the cost of comparable feed mixture by applying two sets of functional units: 100 slaughter pig feed units and 1 kg of pig live weight. Results and discussion: A similar relationship between cost and GWP impact was observed across all methods, although variability of GWP impact magnitude depending on method was observed. Reducing at an equivalent cost, GWP reduction ranged from 5.6 to 27% based on the pig feed functional unit, and 2.4 to 13% based on the pig live weight functional unit. Optimizing feed mixtures for GWP impacts resulted in significantly increased contributions to other impact categories, including a 56% increase in terrestrial ecotoxicity. Despite the increased contributions to other impact categories, all optimized feed mixtures achieved a reduction in endpoint indicators and single score. Endpoint reductions to the feed unit were 2.3–25% for ecosystem damage, 7.4–15% for human health, and 6.0–16% based on a single score value. Conclusions: The findings emphasize the key importance of addressing LUC when optimizing the GWP of agri-food production. Suggestions are provided for areas of improvement in future optimization studies applying a dietary unit as the objective function, including additional midpoint impact categories and/or extended optimization covering whole areas of protection. The findings suggest that GWP impacts may be reduced at no additional cost if included or embedded in the pig feed formulation procedure.