The aim of this observational cohort study was to investigate the potential economic impact of subclinical bovine herpesvirus 1 (BoHV‐1) infection in a commercial UK dairy herd in terms of milk yield depression. Infection status of cows (infected or not infected) was assigned from serology on a single occasion. A multi‐level linear model was used to evaluate the impact of infection status on milk production, using milk records that were routinely collected over two years. BoHV‐1 seropositive cows produced 2.6 kg/day less milk over the study period compared with cows that were seronegative. This result highlights the importance of appropriate management of risks associated with subclinical infection with BoHV‐1 as part of proactive herd health and production management.