Space allowance and dietary fibre shape distinct adaptive proteomic responses in muscle and measurable effects on broiler meat quality

The poultry industry faces increasing demand for sustainable production aligned with meat quality and animal welfare. This study examined effects of space allowance (39 vs. 21 kg/m²) and dietary fibre (DF) supplementation (control vs. DF) on broiler pectoralis major muscle using mass spectrometry-based proteomics under higher-welfare conditions. While yield characteristics were unaffected, reduced space allowance significantly increased intramuscular fat and altered the proteome, with enrichment of proteins in oxidative phosphorylation, transcriptional stress and shifts in carbohydrate metabolism. Broilers receiving DF exhibited lower physical activity and feeding behaviours, with proteomic profiles linked to glycolysis, glycogen turnover and muscle architecture, as well as with reduced drip loss regardless of space allowance. Under higher space, DF induced broader proteomic adaptations, including cytoskeletal remodelling, lipid biosynthesis regulation and vascular homeostasis. These findings highlight how husbandry factors interact to shape meat phenotypes, offering a molecular framework to support quality-focused, welfare-aligned and environmentally conscious meat production.