LAUSR

ABSTRACT This study was done to evaluate the effects of two dietary probiotic preparations (Bacillus subtilis and Bacillus licheniformis) on growth performance, intestinal microbiota, nutrient digestibility and cytokine gene expression in broiler chickens. A total of 180 male broiler chicks (one-day-old Ross 308 strain, average initial body weight = 40.05 ± 0.12) were used in a completely randomized design (CRD) composed of 3 treatments and 6 replicates. Experimental diets included: (1) basal diet (without additive), (2) basal diet plus 0.5 g/kg diet B. subtilis preparation (1 × 109 CFU/g), (3) basal diet plus 0.5 g/kg diet B. licheniformis preparation (1 × 109 CFU/g). The results showed that supplementation of B. licheniformis improved (P < 0.05) broilers’ body weight gain (BWG), feed conversion ratio (FCR), and production efficiency factor (PEF). Adding B. licheniformis caused the lowest (P < 0.01) feed cost per kilogram weight gain and the highest (P < 0.05) return of investment (ROI). Probiotic treatments significantly decreased (P < 0.01) ileal pH of the broilers. Probiotic treatments improved (P < 0.01) apparent metabolizable energy (AME) and total tract digestibility of protein. It was concluded that although both probiotic bacteria improved AME and total tract protein digestibility, B. licheniformis was superior to B. subtilis in improving broiler chickens’ BWG (2580.70 vs. 2427.45 g) and their PEF (418.95 vs. 374.49).