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Background: Infectious bovine keratoconjunctivitis (IBK) in beef cattle has major welfare and production implications. Effective vaccination against IBK would also reduce antibiotic use in beef production., Objective/hypothesis: To evaluate the efficacy of a conditionally licensed commercial IBK vaccine containing Moraxella bovoculi bacterin. Primary working hypothesis was that animals vaccinated with 2 doses of the commercial M. bovoculi vaccine would have a lower risk of disease., Animals: Spring born calves at a university cow-calf herd. After excluding animals with ocular lesions, calves eligible for prevention assessment in 2017 and 2018 were 163 (81 vaccinated, 82 unvaccinated) and 207 (105 vaccinated, 102 unvaccinated). One hundred sixty two and two hundred and six calves completed the follow-up period in 2017 and 2018, respectively., Methods: A randomized controlled trial. The trial design was a 2-arm parallel trial with a 1:1 allocation ratio., Results: In both years, calves receiving the vaccine had more IBK. This effect was small. The pooled risk ratio was 1.30 (95% confidence interval 0.84-2.01). The pooled unadjusted difference in mean weight (kg) at weaning was -0.88 (95% confidence interval-7.2-5.43)., Conclusions and Clinical Importance: We were unable to document that the M. bovoculi bacterin vaccine had a protective effect for the incidence of IBK in our single herd in a 2-year study., (© 2019 The Authors. Journal of Veterinary Internal Medicine published by Wiley Periodicals, Inc. on behalf of the American College of Veterinary Internal Medicine.)