Estimation of the Availability and Effect of Some European Agro-Industrial By-Products to Reduce the Carbon Footprint of Sheep and Goat Diets

In this study, we aimed to assess the availability and environmental impact of a selection of widespread agro-industrial by-products in Europe and their potential to reduce the environmental impact of small ruminant diets by replacing conventional feed ingredients. Grape, olive, and tomato pomaces and spent grains of beer were considered. The carbon footprint of products (CFP) was used to quantify the environmental impact of agro-industrial by-products, according to the ISO 14067:2018 standard. The system boundary was defined as gate-to-gate, and 1 kg of dried by-product was chosen as the functional unit (FU). The system included the relevant stages of agro-industrial by-product production, from the process of drying agro-industrial by-products to the treatments carried out in the feed industry (e.g., milling, mixing, and pelleting). The CFPs of grape, olive, and tomato pomaces and spent beer grains were 0.26, 0.22, 0.31, and 0.21 kg CO2 equivalents (CO2e)/FU, respectively. Under the assumptions adopted in this scenario-based assessment, reusing grape, olive, tomato, and brewery industry by-products as partial replacements for conventional feed ingredients in sheep and goat diets reduced diet CFP by an average of 23%, with an estimated mitigation potential of 5.15 Mt CO2e. These values should be interpreted as model-based estimates rather than as directly generalizable mitigation outcomes, because they depend on the selected system boundary, drying assumptions, emission factors, transport exclusion, and the practical feasibility of the dietary substitutions considered. Overall, the results suggest that the recovery of selected agro-industrial by-products may contribute to reducing the environmental impact of conventional feed ingredients when appropriate preservation, logistics, and diet formulation conditions are met.