Antibody levels and immunity to infectious bovine rhinotracheitis virus (IBR) infections in Wisconsin dairy cattle.

Individual cows and calves in 7 Holstein-Friesian herds with a history of respiratory disease in Green County, Wisconsin, USA, were swabbed intranasally and bled monthly, some for periods over 1 year. Virus isolation and serological procedures were completed on the samples in an attempt to recognize the problems and peculiarities that IBR virus continues to cause in dairy cows, in spite of, and possibly because of vaccines available for immunization against this agent. While IBR virus was isolated from animals on 6/7 farms over the period of study the history of vaccination with Nasalgen IP prevented the differentiation of vaccine (avirulent) virus from field (virulent) virus. IBR virus was isolated from apparently healthy animals as well as animals having signs of respiratory disease. IBR virus was assumed to be the cause of recurrent respiratory disease and ocular disease on at least two of the farms studied as established by virus isolation, serology, and the presence of characteristic signs of respiratory disease. While IBR virus was present on the other five farms its precise role in the diseases observed was not determined. IBR virus, whether vaccine virus or field virus, appeared to be persistent in 6/7 of the herds studied. Keratoconjunctivitis and corneal ulceration were the only signs of disease in animals in one herd where the etiologic agent was presumed to be field strain IBR virus. Antibody to IBR virus did not protect animals from respiratory or ocular disease in which IBR virus was thought to be a causative agent. Adult animals that had antibody to IBR virus at the time of vaccination with Nasalgen IP generally did not respond after vaccination with an increase in IBR virus antibody. Those adults that did not have antibody prior to vaccination, generally responded to vaccination with a rise in antibody. Vaccination of calves with Nasalgen IP generally did not cause an increase in antibody. IBR virus antibody was higher in vaccinated herds with recurrent respiratory disease.