Using an in vitro co-infection model of BRSV and M. haemolytica to model BRDC, we further demonstrate that BRSV-induced expression of IL-17 is significantly exacerbated in the presence of secondary bacterial exposure to M. haemolytica, suggesting a mechanism that may be contributing to neutrophilia in the lungs of calves with BRDC. This evidence concerns the gene IL17A and coinfection.