infC gene encodes the translation initiation factor IF3 in bovine Pasteuella multocida,but it whether or not regulation to the virulence and cross-protection in P.multocida is still not well understood.In this study,the infC gene mutant(△infC)derived from bovine P.multocida type A strain CQ2 was constructed using by homologous recombination method.Compared with wild strain,the △infC showed significant increasing in biofilm formation,but the capsule produc-tion,virulence and bacterial loading in organs were significant decreased,and the IL-1β secretion of mouse peritoneal macrophage increased.Along with the infC gene deletion,the expression of genes related to capsule synthesis and LPS synthesis and transport were significantly down-regulated,while that of genes related to biofilm synthesis and outer membrane protein were significantly up-regulated.The inactivated vaccines of wild type and mutant were prepared and mice were immu-nized twice then challenged with wild type strains,respectively.The immuno-protection rate of△in fC inactivated vaccine against bovine P.multocida type A,B and F were 100.0％,83.3％and 0.0％,respectively,and the immuno-protection rate that against rabbit type P.multocida was 33.3％.The results indicated that infC gene could affect the virulence of P.multocida by regula-ting the production of capsule and the expressions of virulence related factors,and the deletion of infC gene conferred a certain cross-protection property of strains.This study provided a certain foundation for the development of P.multocida vaccine.