In this study Mentofin® was used in commercial broiler chickens naturally exposed to infectious bursal disease virus (IBDV) and administered live Newcastle disease virus (NDV) vaccine to evaluate the ability of Mentofin® to reduce Escherichia coli-related respiratory lesions, immunomodulate Newcastle disease (ND) vaccine response, change pharyngeal aerobic bacterial counts, and have certain impacts on specific production parameters. Mentofin® was added to the drinking water (100 ml/500 l water) of broiler chickens aged between 3 and 5 days. ND and IBD vaccinations were administered via drinking water to 15-day-old chickens. NDV vaccination was given again when the chickens were 20 days old. No difference was found between the control and Mentofin® groups regarding oropharyngeal aerobic bacterial counts. Acute IBD was diagnosed in both groups because the antibody levels were unprotective and varied widely. The mean NDV-hemagglutination inhibition antibody titers obtained with NDV vaccination in both groups were above the protective level, and the titers were considered uniform. The data showed that Mentofin® was able to reduce the lesions caused by E. coli after NDV vaccination. Mentofin® also reduced the rate of mortality in broilers with IBD interaction to the live NDV. In conclusion, Mentofin® reduced both the occurrence of E. coli-related lesions and the mortality rate usually observed after administering live NDV to broilers with clinical IBD.