Antibody responses to IBR vaccination in feedlot cattle

Infectious Bovine Rhinotracheitis (IBR) is an important respiratory disease of cattle. The disease has been especially critical in western feedlots and IBR virus infection has been associated with the shipping fever complex. Numerous commercial vaccines are in wide use to prevent this disease. Experimentally, these vaccines have been shown to be immunogenic and effective in preventing clinical IBR. A large western feedlot has routinely used a modified live virus IBR vaccine in all cattle entering the feedlot. Despite vaccination, the feedlot continued to experience significant morbidity and mortality associated with respiratory disease. A major portion of this respiratory disease was believed to be IBR virus infection. This study was designed to study immunity to IBR virus of cattle as they enter the feedlot, and to measure the immune responses of feedlot cattle to intramuscular modified live virus IBR vaccines under field conditions. Immunity to bovine parainfluenza type 3 (PI3) virus upon arrival at the feedlot and seroconversion to that virus as a result of natural infections was also studied.