Legume substitution alone is not enough: A multi-criteria LCA of low-soybean meal broiler feed systems

The study evaluated the effect replacing soybean meal with UK-grown legumes and sunflower meal and enzyme supplementation on environmental impact of broilers. A total of 960 male broilers (Ross 308 and JA787) were assigned to five diets, high nutrient density (HN), moderate nutrient density (MN), a legume-based MN diet without enzymes (LEG), and LEG supplemented with standard (LEG-STD) or super-dose (LEG-S) NSP enzymes. In LEG diets, a mix of pea, bean, lupin, and sunflower meal at equal proportions replaced 50% of SBM in MN. The enzyme mix contained 0.01% phytase and 0.01% Signis, while the super-dose mix contained 0.05% phytase and 0.015% Signis. Pen-level life cycle assessment of consumed feed was normalised to meat yield (1 bird/pen at D35 for Ross 308 and D42 for JA787) with legumes produced under conventional or low fertilisation and plant protection input legume production scenarios. Impact categories included global warming potential with land use change (GWP), freshwater eutrophication (EUT), terrestrial acidification (ACID), ecotoxicity (ETOX), land use (LU), and water resource depletion (WRD). Data was analysed following 5 × 2 full factorial design. Legume based diets had significantly lower GWP compared to HN regardless of bird strain (P < 0.05) while meat yield was not significantly affected, however, these diets had significantly higher LU and ETOX compared to HN. When legumes were produced under low-input conditions, the difference between LEG-S and HN became insignificant (P > 0.05), however, the diet still have significantly higher ETOX (P < 0.05). These findings highlight trade-offs in feed-based mitigation and support integrated agronomic and nutritional strategies.