We investigated the immune responses against bovine herpesvirus type 1 (BHV-1) and bovine viral diarrhea virus (BVDV) by two different vaccination protocols. An attenuated-live vaccine (containing BHV-1 and BVDV-1) and an inactivated vaccine (containing inactivated virus antigens of BHV-1, BVDV-1, and BVDV-2) were used. Two different immunization protocols were investigated: inoculation of live vaccine 28 days after inactivated vaccine inoculation (KL), and inoculation of inactivated vaccine 28 days after live vaccine inoculation (LK). Antibodies against BHV-1, BVDV-1, and BVDV-2 were examined. Antibody titer against BHV-1 was significantly higher in calves vaccinated by the KL protocol 30 days post inoculation (dpi). On the other hand, antibody titer against BVDV-1 was significantly lower in calves vaccinated by the KL protocol 30 dpi. However, approximately equivalent antibody titers were observed using either protocol by 56 dpi. No significant difference in antibody titer against BVDV-2 was observed between the two protocols, with a nearly equivalent immune response acquired by 56 dpi. These results suggest that when combination vaccines are used, the vaccination protocol should be selected depending on the prevalence of infectious diseases in each farm
