Observations on an outbreak of infectious bovine rhinotracheitis in a bull test station.

A clinical outbreak of infectious bovine rhinotracheitis with a morbidity of 11.3% in unvaccinated bulls of a test station is described. The outbreak began explosively in one pen and appeared in others over a period of two weeks. After intranasal vaccination of all bulls, the sporadic occurrence of clinical infectious bovine rhinotracheitis ceased. Although no animals died as a result of infectious bovine rhinotracheitis, the periodic weighing necessary in a bull test station revealed that affected bulls were set back in their average daily rate of gain. While on test, affected Angus bulls never returned to an average daily gain comparable to unaffected bulls of the same breed.