THE present study evaluated the potential of Mannan-oligosaccharides & β-glucan (MOS-βG) and Saccharomyces cerevisiae yeast, administered individually or in combination, to mitigate the adverse effects of high stocking density on growth performance, intestinal histomorphometry, and gene expression related to muscle development in growing New Zealand White rabbits. A total of 108 six-week-old male NZW rabbits (weighing 938.42 ± 18.15 g) were randomly allocated to eight groups arranged in a 2 × 4 factorial design, representing two stocking densities (12 and 24 rabbits/m²) and four dietary treatments: control, MOS-βG (1 ml/L water), S. cerevisiae (1 g/L water), and their combination. Each treatment included three replicates. Both additives significantly improved growth performance parameters compared with the control groups. However, the combined MOS-βG and S. cerevisiae produced the most pronounced improvements in body weight (BW), body weight gain (BWG), total feed intake (TFI), and feed conversion ratio (FCR) under both stocking densities. Under HSD, the combined treatment significantly improved intestinal morphology, evidenced by the greatest villus height (1784 µm) and a more favorable villus height-to-crypt depth ratio compared with the control and single-supplement groups. Decreased expression of MSTN, enhanced expression of MYF5, IGF-1 were found in groups fed with MOS-βG, S. cerevisiae ; the best results were in the combined treatment groups under both densities. Overall, these findings demonstrate that dietary supplementation with MOS-βG and S. cerevisiae, particularly when combined, effectively alleviates the negative consequences of stocking density stress by enhancing growth performance, preserving intestinal architecture, and improving growth-related genes in growing rabbits.