Background: Bovine herpesvirus-1 (BoHV-1), the causative agent of infectious bovine rhinotracheitis (IBR), genital infections, and abortion, is one of the most economically significant pathogens in the dairy industry. The virus’s ability to establish latent infection and reactivate under stress makes its control and eradication challenging. In Iran, BoHV-1 seroprevalence in dairy herds is often high and endemic, while systematic control programs remain limited. Objective: To investigate the dynamics of BoHV-1 antibodies in bulk tank milk (BTM) of a large Holstein dairy herd (1,500 head) in Nishapur, during the transition from acute outbreak (May 2024) to stable endemic status, over a 21 month monitoring period (March 2024 to November 2025). Methods: After confirming viral presence by PCR in nasal and conjunctival swabs, BTM samples were tested monthly using indirect ELISA (IDVET kit). Inactivated vaccination (HIPRABOVIS-3®) was applied only to heifers and calves. Results: Prior to the outbreak, antibody titers in BTM were very low, indicating high susceptibility in the herd. With the onset of clinical signs, widespread seroconversion and a sudden rise in titers were observed. In the long term (up to November 2025), titers remained consistently high, reflecting the establishment of natural herd immunity. Conclusion: Long-term BTM monitoring is a sensitive, cost-effective, and practical tool for tracking BoHV-1 infection dynamics, especially in large herds. Despite herd immunity, the risk of latent virus reactivation persists. Progress toward sustainable control and eradication requires the use of marker vaccines (gE-deleted DIVA), individual screening (particularly of replacement heifers), removal of latent carriers, and implementation of a coordinated national program.

Keywords