| Summary: | A total of 700 broiler chicks (350 Indian River and 350 Ross 308) were obtained from a local hatchery. Birds were randomly allocated in a completely randomized design by strain into two dietary groups: a control group (corn–soybean meal) and a treatment group in which 7.5% of soybean meal (SBM) was replaced with fermented soybean meal (FSBM). Each group included 175 birds, distributed across seven replicates (pens) with 25 birds per pen. Birds were weighed at the start of the trial and at the end of each rearing phase (starter (1–14 days of age), and grower phases (15–35 days of age)). Mortality was monitored daily throughout the experiment. Weekly feed intake was recorded for each pen. On day 35, 14 birds were randomly selected from each treatment–strain combination for carcass and meat quality evaluation. Data were analyzed with linear models; strain, diet, and their interaction were the investigated effects. No strain–diet interaction was detected for growth performance, carcass and meat quality, and intestinal morphology traits (<i>p</i> > 0.05). Significant interaction effect on crude protein digestibility is found (<i>p</i> < 0.001). The FSBM improved crude protein digestibility for the Indian River broiler strain, while the opposite occurred in the Ross 308 strain. Fermented soybean meal supplementation did not significantly affect body weight gain, feed conversion ratio (FCR), or feed intake during the study period (<i>p</i> > 0.05). The Ross strain exhibited a higher dressing percentage (<i>p</i> = 0.04) and greater cooking loss (<i>p</i> = 0.01), whereas the Indian River strain showed higher abdominal fat percentage (<i>p</i> = 0.04) and shear force (<i>p</i> = 0.003). The dressing percentage, pH, color parameters, cooking loss, water-holding capacity, and breast fillet yield for FSBM and control groups did not differ (<i>p</i> > 0.05). Ileum villus length and width were significantly higher (<i>p</i> < 0.05) in the FSBM group compared to the control group. In conclusion, Fermented soybean meal can enhance intestinal morphology and crude protein digestibility in a strain-specific manner; however, its impact on growth and carcass attributes is limited at this inclusion level.
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