Efficacy of a combination modified-live IBR-BVD-PI3- BRSV vaccine + Mannheimia haemolytica toxoid against challenge with virulent bovine respiratory syncytial virus (BRSV) in young calves 60 days of age

Efficacy of attenuated (att) bovine respiratory syncytial virus (attBRSV) as an antigen fraction in a multivalent 6-way vaccine containing modified-live virus and an inactivated Mannheimia haemolytica bacterin-toxoid was given as a single subcutaneous injection, and evaluated by an aerosol challenge by nebulization in young calves with virulent BRSV strain 21 d after vaccination. A total of 32 Holstein calves, seronegative to BRSV and 60 days-of-age at the time of vaccination, were used in the study. Calves were allocated to 2 treatment groups with 16 animals per group, and received either a single dose of a modified-live bovine herpes virus-1, bovine viral diarrhea virus, parainfluenza 3 virus, bovine respiratory syncytial virus vaccine + M. haemolytica bacterin-toxoid, or corresponding placebo formulation without targeted BRSV antigen. Administration of the 6-way vaccine containing BRSV fraction induced significantly higher virus-neutralizing antibody (p=0.0003) and anti-BRSV IgG titers (p=0.0006) in vaccinated animals compared to the placebo group. Consequently, BRSV-vaccinated calves had significantly (p<0.0001) higher arterial partial pressures of oxygen (PaO2), significantly (p<0.0001) lower percentage of lung lesions, and significantly reduced mortality rate (p<0.0001) than did placebo vaccinated calves subsequent to BRSV challenge. Furthermore, there was a 61.2% reduction in virus shedding and duration of shedding (p<0.0001), indicating strong vaccine efficacy.