The effects of probiotics and postbiotics on immunity, microbiome, and oxidative stress in broiler chickens vaccinated with Salmonella kentucky

Objective: The study aims to evaluate the effects of Bacillus sp. spores-based probiotics and postbiotics, administered via drinking water in addition to an inactivated Salmonella Kentucky vaccine, on broiler chickens. Salmonella Kentucky, a highly contagious pathogen in the poultry industry, poses a significant risk to human health, causing fatalities upon transmission. This research seeks to determine the impact of these supplements on antioxidant/oxidant parameters as indicators of oxidative damage in liver and kidney tissues, to assess potential differences in bacterial load by examining fresh fecal microbiota, and to measure antibody titers to evaluate the effects of the organic supplements on the immune system. Material and Methods: This study was carried out at the Poultry Research Unit of Aydın Adnan Menderes University, Faculty of Veterinary Medicine. In this trial, a total of 130 broiler chicken (Ross 308) were used. All chicks were vaccinated with inactivated vaccine S. Kentucky prepared by the Department of Microbiology of the faculty on the 7th and 21st days, respectively (booster dose). The groups were randomly divided into five groups. Water without additives was given for the control and only the vaccine-administered group; in the remaining three groups, drinking water was supplemented as such: in one group, water was mixed with a probiotic from Bacillus subtilis, in the second group, water was mixed with a postbiotic from Bacillus subtilis, while in the third group, the water was mixed with the combination of both probiotic and postbiotic of Bacillus subtilis; all the above was added to plastic drinkers. On the day of blood and organ sampling, broilers were anesthetized with Ketamine and euthanized with cervical dislocation on the 21st and 42nd days. For checking the antibody titers, 2 mL of blood was collected from the neck region and then a tube agglutination test was conducted. Further, for determining the oxidative stress parameters on the slaughter days, the concentration of TP, SOD, CAT, GSH, and MDA was determined in liver and kidney tissues. Intestinal xiv microbiota changes were determined by microbiome analysis, which was performed with fresh fecal samples taken from the groups. Results: The probiotic and postbiotic-supplemented groups had increased immune parameters, improved microbial diversity, and decreased markers of oxidative stress. The immune response rises in the vaccinated groups, and this effect was amplified by probiotic and postbiotic supplementation. Microbiome analysis was capable of determining an increase in beneficial bacterial ratios and a decrease in toxic bacterial ratios. In probiotics and postbiotics groups, MDA levels declined while the activity of antioxidant enzymes (SOD, CAT) and GSH increased. Conclusion: Apart from vaccination, supplementation of drinking water with Bacillus subtilis as a probiotic and postbiotic in broiler chickens was found to exert immune-supportive, microbiota-regulating, and oxidative stress-reducing effects. These results suggest that probiotics and postbiotics can enhance vaccine efficacy and are important supportive agents in maintaining the health of broiler chickens. Keywords: Salmonella Kentucky, Vaccine, Bacillus subtilis, Immune system, Microbiome, Microbiota, Probiotic, Postbiotic, Oxidative Stress, Broiler.