Toward lower-carbon dairy: Life cycle assessment of a modelled high-yielding Swedish dairy farm

• Feeding strategies significantly affected total farm greenhouse gas emissions. • By-product and domestic diets lowered total emissions versus the commercial strategy. • By-product and domestic diets lowered total land use versus the commercial strategy. This study used systems analysis to quantify farm-level greenhouse gas (GHG) emissions and land use (LU) from a high-yielding Swedish dairy farm under six feeding strategies, using a cradle-to-farm-gate attributional Life Cycle Assessment. The strategies combined three dairy cattle concentrate mixes: commercial (COM), by-products-based (BYP), and based on domestically produced feed ingredients (DOM), with two roughage strategies for replacement heifers: grass-clover silage (GS) or a 50:50 dry matter basis roughage mix (RM) of GS and whole crop cereal silage. All rations were formulated using the Nordic feed evaluation system and standardised for equal energy-corrected milk (ECM) output. Values on enteric methane emissions and animal productivity were based on animal trials with direct measurements on animals offered these diets. Compared to COM, total farm GHG decreased more under BYP (GS: -6.0%; RM: -5.9%) than under DOM (GS: -2.6%; RM: -2.1%). Under the BYP strategy, LU decreased by 3.8% for both GS and RM compared to COM. Conversely, the DOM strategy increased LU by 0.3% (GS) and 6.8% (RM) compared to COM. Using a RM instead of GS in the heifer rations increased GHG emissions by 0.9%, 1.0% and 1.5% and reduced LU by 7.9%, 8.2%, and 1.3% for the COM, BYP, and DOM strategies. The results highlight the importance of accounting for the carbon footprint and LU differences of feed ingredients when designing sustainable dairy systems. Feed-based mitigation strategies, involving by-products and domestically sourced ingredients, offer practical, immediate opportunities to reduce emissions in Swedish and other Northern European dairy systems, without compromising productivity.