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The use of agro-industrial by-products in animal feed is an opportunity to reduce imports, food waste and promote a clean and circular economy, turning worthless raw materials into high-quality and low-cost animal feeds, which does not compete with human food. This study aims to produce silages with by-products of carrot, sweet potato, potato, and tomato pomace and integrate them in lamb diets, replacing 50% of dry matter (DM) of a concentrate-based diet. Effects on growth performance, meat quality and methane production were evaluated. Three silages were produced using 350 g/kg tomato pomace, 200 g/kg wheat bran, 150 g/kg alfalfa hay and 300 g/kg potato (Psil) or 300 g/kg sweet potato (SPsil) or 300 g/kg carrot (Csil). Thirty-two lambs were housed individually and divided into four groups (8 animals/group) on the following diets: Control - 850 g/kg concentrate and 150 g/kg hay; P - 500 g/kg concentrate and 500 g/kg Psil in DM; SP – 500 g/kg concentrate and 500 g/kg SPsil in DM; C – 500 g/kg concentrate and 500 g/kg Csil in DM. The trial lasted 6 weeks after 1 week of adaptation. Methane production was assessed in vitro by the Ankom system, using as inoculum rumen content samples collected individually from 6 lambs on each diet at slaughter. Diet had no effect on DM intake, average daily gain and DM conversion ratio, averaging 1055 ± 248 g, 320 ± 61.1 g and 3.35 ± 0.600, respectively. Also, carcass characteristics were not affected by the diet except for the lightness of subcutaneous fat which was increased by the silage diets (L* value, P = 0.016). The meat parameters, pH, intramuscular fat, shear force, cooking losses and sensory attributes, were not affected by the diet. In meat color, the parameters a* and Chroma were highest in animals fed diet C, have an intermediate value with Control diet and are lowest with diets P and SP (P = 0.027 and P = 0.012 , respectively). Diets had no impact on total methane emissions. The costs of the silage diets per kg live weight gain were lower than those of Control diet (P = 0.018). In summary, by-product silage can be a good option to replace concentrated feed in lamb diets without altering the growth performance and meat quality or methane production and thus contributing to the sustainability of livestock farms and the environment. • Tomato pomace, potato, sweet potato and carrot wastes can be used in lamb diets. • Ensiling in mixtures is a good strategy to preserve these byproducts. • Byproduct silages can partially replace concentrate feeds in lamb diets. • Byproduct silages can reduce feed price and improve environmental sustainability. [ABSTRACT FROM AUTHOR]