Abstract: [Objective] To evaluate the safety and immunoprotective efficacy of the infectious bovine rhinotracheitis virus （IBRV） vaccine candidate strain IBRV/JSM. [Methods] Ten healthy calves aged 4-5 months were randomly divided into a control group and a vaccination group, with five calves in each group. Calves in the vaccination group were intramuscularly injected in the neck with 1 mL/head of candidate strain IBRV/JSM containing 10^5.0 TCID₅₀/mL, while calves in the control group received 1 mL/head of PBS in the neck. Clinical symptoms were recorded, and serum samples were collected to measure IBRV neutralizing antibody titers and analyze PCR detection results of IBRV nucleic acid. At 28 days post-immunization, both groups were challenged with IBRV/LN01-08 strain F5 seed virus containing 10^6.8 TCID₅₀/mL. Rectal temperatures of the calves were measured after challenge, and clinical signs of the calves were observed and recorded after challenge. [Results] Neutralizing antibody titers in the control calves remained <1∶ 2 within 28 days post-immunization. In the vaccinated calves, titers increased to 1∶28 at 14 days post-immunization, peaked at 1 ∶ 46 at 21 days post-immunization, and decreased to 1∶ 26 at 28 days. No abnormal clinical signs were observed in either group, and all serum PCR results were negative. After challenge, only one calf in the vaccination group showed a body temperature increase of more than 1 ℃ above the baseline, whereas all 5 calves in the control group exhibited elevated body temperature accompanied by typical IBR symptoms such as ocular and nasal discharges. [Conclusion] The vaccine candidate strain IBRV/JSM demonstrates good safety and immunogenicity and has the potential to serve as a novel vaccine candidate strain for the prevention and control of infectious bovine rhinotracheitis in calves.

Key words: infectious bovine rhinotracheitis, attenuated live vaccine, safety, immunogenicity, neutralizing antibody titer