This study was planned to evaluate the immunomodulatory potential of Streptomyces and Bacillus-based probiotic formulations in broiler chickens. Day-old (n=90) broiler chicks were randomly allocated to six experimental groups (n=15 each), including: Group A served as a negative control; Group B was administered with Streptomyces sp. @ 1×10⁹ CFU/kg; Group C was administered with Bacillus sp. @ 1×10⁸ CFU/kg; Group D was administered a commercial probiotic (Probio^TM) @ 2g/kg; Group E was administered with Streptomyces sp. and Bacillus sp. @ 1×10⁹ CFU and 1×10⁸ CFU/kg, respectively, and Group F was administered with Streptomyces sp., Bacillus sp. and E. coli Challenge @ 1×10⁹ CFU/kg, 1×10⁸ CFU/kg and 3×10⁷ CFU/mL of broth culture, respectively. The treatments were given in feed from day seven till the Day 42 of age. The results indicated more pronounced immunostimulatory effects in the Streptomyces-Bacillus combination (Group E) those were evident by significant increase (P<0.05) in the absolute weight of the immune organs as compared to the control. Cellular immunity based on phagocytic activity in the carbon clearance assay revealed two folds higher values as compared to control in the probiotic supplemented groups and lymphoproliferative response was also sustainable in these groups.   Humoral immune responses also revealed that the probiotic combination enhanced both primary (IgM) and secondary (IgG) antibody responses, with 37% higher IgG titers against sheep RBCs and 25% higher NDV vaccine titers (P<0.05). Furthermore, the probiotic combination conferred better protection against E. coli challenge and prevented the lymphoid organ atrophy typically associated with bacterial infection. Histopathological examination confirmed these functional improvements, revealing well-developed germinal centers (white pulp) in the spleen, cortical hyperplasia in the thymus, and follicular hypertrophy in the bursa of probiotic-fed birds. These findings collectively demonstrate that the Streptomyces-Bacillus probiotic combination effectively enhances both innate and adaptive immunity in broilers.

To Cite This Article: Chen H, Kanwar N, Khaliq S, Saleemi MK, Waheed N and Khan A, 2026. Investigations on the immunomodulatory effects of streptomyces and bacillus-based probiotics in broilers. Pak Vet J. http://dx.doi.org/10.29261/pakvetj/2026.002