Impacts of locally isolated <i>Bacillus subtilis</i> and <i>Bacillus spizizenii</i> on growth performance, carcass traits and intestinal architecture of Ross 308 broiler chickens

This study investigated the probiotic effects of Bacillus subtilis DK1-SA11 (T1), Bacillus spizizenii B-3541 (T2) and their mixture (T3) on Ross 308 broilers. Initially, 200 one-day-old chicks were allocated to four groups (T0, T1, T2 and T3; n = 50/group, 4 replicates). After weak birds were excluded within 48 h to ensure uniformity, each replicate maintained 12 birds (n = 48/group). The control (T0) group received no Bacillus, while the treated groups received strains through drinking water until day 42. Probiotic supplementation significantly improved performance. T2 improved the overall feed conversion ratio compared to T0 (P < 0.05). Regarding meat quality, probiotics enhanced water-holding capacity, significantly reducing cooking loss at T1 and the amount of expressed juice at T2 (P = 0.0002), indicating improved tenderness. Furthermore, supplementation significantly improved jejunal architecture; T3 showed the highest villus length-to-crypt depth ratio at day 42, primarily because of significantly reduced crypt depth (P = 0.0001). In conclusion, oral supplementation with local B. subtilis DK1-SA11 and B. spizizenii B-3541 effectively enhances feed efficiency, meat tenderness and intestinal architecture in broiler chickens.