The aim of this study was to test in vitro the ability of a mixture of citrus extract, maltodextrin, sodium chloride, lactic acid and citric acid (AuraShield L) to inhibit the virulence of infectious bronchitis, Newcastle disease, avian influenza, porcine reproductive and respiratory syndrome (PRRS) and bovine coronavirus viruses. Secondly, in vivo, we have investigated its efficacy against infectious bronchitis using a broiler infection model. In vitro, these antimicrobials had expressed antiviral activity against all five viruses through all phases of the infection process of the host cells. In vivo, the antimicrobial mixture reduced the virus load in the tracheal and lung tissue and significantly reduced the clinical signs of infection and the mortality rate in the experimental group E2 receiving AuraShield L. All these effects were accompanied by a significant reduction in the levels of pro-inflammatory cytokines and an increase in IgA levels and short chain fatty acids (SCFAs) in both trachea and lungs. Our study demonstrated that mixtures of natural antimicrobials, such AuraShield L, can prevent in vitro viral infection of cell cultures. Secondly, in vivo, the efficiency of vaccination was improved by preventing secondary viral infections through a mechanism involving significant increases in SCFA production and increased IgA levels. As a consequence the clinical signs of secondary infections were significantly reduced resulting in recovered production performance and lower mortality rates in the experimental group E2.