Improving efficiency and reducing environmental impacts pose challenges to Mediterranean livestock systems, with few viable alternatives to conventional forages. This study evaluated cucumber–straw silage (SIL) as an alternative forage to oat hay (HAY) for lamb production using integrated in vitro , in vivo , and life-cycle assessment approaches. An in vitro fermentation study was conducted by progressively replacing concentrate with SIL or HAY, and rumen fermentation, and CH 4 production were measured over 144 h. Subsequently, a 12-week in vivo trial was conducted on a commercial farm with 450 lactating Segureña ewes and 610 lambs to assess productive performance and metabolic status. In vitro experiment followed a factorial design (two forage types × four inclusion levels) within a completely randomized design, while in vivo experiment applied a completely randomized design . In vitro results showed that a 50% inclusion of SIL maintained rumen fermentation activity comparable to HAY in terms of gas production and volatile fatty acid concentrations; moreover, SIL shifted fermentation toward higher butyrate (+13.3%; P = 0.001) and lower CH 4 emissions (−17.3%, interaction P = 0.007). In vivo, SIL supported comparable animal performance to HAY, with no significant differences in lamb growth (210 vs. 215 g/day), ewe body condition score, or health, as blood metabolites remained within physiological ranges. A cradle-to-farm-gate life cycle assessment, following ISO-14044 standards and applying two allocation approaches for cucumber waste, revealed that under a zero-allocation scenario (treating waste as burden-free), greenhouse gas emissions averaged 9.50 CO 2 -eq/kg liveweight (95% CI: 8.29–13.6) compared with 11.6 (95% CI: 10.1–15.9) for HAY, alongside reductions in land occupation of 50%, and water consumption of 70%. Therefore, SIL presents an effective strategy to valorise horticultural waste while maintaining productivity and potentially improving the environmental performance of Mediterranean lamb systems. Further validation across diverse management conditions and by-product sources is recommended. • A circular bioeconomy strategy based on replacing oat hay by cucumber-straw silage was evaluated. • The silage reduced CH 4 by 17.5% through shifts in rumen fermentation. • Lactating ewes and lambs maintained similar performance and health indicators. • Zero-allocation LCA showed an 18% reduction in GHG emissions through waste valorisation. • Land use decreased by 50% and water use by 70% when oat hay was replaced with silage.
Hassan et al. (Fri,) studied this question.