Transparent and harmonized allocation factors for crop-processing co-products in U.S. dairy rations

Abstract Purpose Crop-processing co-products are widely used in U.S. dairy rations and contribute substantially to feed supply, yet the allocation factors needed to assign them a share of upstream crop-production burdens are not harmonized across methods or available in a single transparent resource. Methods This study compiled a database of economic, dry-matter mass, and gross energy allocation factors for 62 dairy-relevant co-products from 22 U.S. plant-processing systems, including small grains, oilseeds, sugar crops, vegetables, and specialty crops, derived from explicit equations applied to harmonized inventory data for 2024–2025. Parametric uncertainty was quantified using Monte Carlo simulation with 10,000 iterations per system and Program Evaluation and Review Technique (PERT) distributed inputs for co-product yields, market prices, and gross energy content, and a cross-method divergence index was used to characterize sensitivity to allocation choice. Results and discussion Of the 62 co-products evaluated, 29 were classified as high sensitivity, 22 as moderate, and 11 as low, with the greatest divergence occurring in almond, sweet corn, citrus, peanut, cotton, and safflower systems. For most co-products, variation across allocation methods exceeded parametric uncertainty within any single method, indicating that allocation choice is the main source of methodological variability in co-product environmental assessment. Conclusion The resulting factors are impact-category neutral and designed to interface with any upstream crop life-cycle inventory, complementing rather than replacing allocations already embedded in general-purpose life-cycle inventory databases.