Impact of Dietary Bacillus toyonensis M44 as an Antibiotic Alternative on Growth, Blood Biochemical Properties, Immunity, Gut Microbiota, and Meat Quality of IR Broilers

Antibiotic-resistant microorganisms may lead to treatment failure and economic losses in the poultry industry and threaten public health. One of the main factors involved in the increasing emergence of antimicrobial resistance is the non-judicious use of antimicrobial agents as growth promoters in poultry and animal production. The search for natural alternatives to growth promoters to antimicrobial agents is continuous and crucial. This investigation focused on the probiotic strains extracted from the gastrointestinal tracts of poultry reared in various habitation types. The selected strain with antioxidant properties was Bacillus toyonensis (BT) M44, used as a probiotic dietary supplement and antibiotic alternative, then investigated its effects on growth performance, blood biochemical parameters, immune response, gut microbiota, and meat quality of IR broilers. Bacillus toyonensis M44 exhibited potent antibacterial activity against MDR microorganisms, as evidenced by MICs ranging from 5% to 10%. A total of 160 IR chicks were allocated into four groups randomly, each consisting of (10 x 4) chicks. The control group was administered a basal diet; the remaining three groups were provided the control diets containing BT at concentrations of 0.4, 0.8, and 1.6 mg/kg. The results indicated that BT-supplemented groups showed increased body weights, weight gain, growth rate, and performance index and reduced feed conversion ratio during the two growth periods compared to control. The best results were obtained with BT 1.6 mg/kg for the antecedent growth metrics. Chicks receiving BT (0.4 mg/kg) had improved renal functions and lower uric acid and creatinine levels than the other groups. Moreover, ALT and AST levels P<0.05 decreased with BT doses compared to the control. BT 1.6 mg/kg produced the best liver function results; the histopathological studies confirmed that BT addition didn't affect the liver and intestine structure. Adding Bacillus toyonensis M44 to the diet formulation improved (P<0.05) lipid profile, immune response, thyroid functions, and gut microflora compared to the control group. Additionally, BT enhanced the chicken meat's juiciness and tenderness characteristics and improved its moisture and protein content; the meat color was also enhanced. Generally, supplementing IR chicken with BT could improve growth performance and blood biochemistry, modulate the gut microflora structure, and enhance the meat quality.