Bovine respiratory syncytial virus (BRSV) is an RNA virus classified as a pneumovirus in the paramyxovirus family. BRSV infections associated with respiratory disease occur predominantly in Young beef and dairy cattle. Initial exposures to the virus are associated with severe respiratory disease; subsequent exposures result in mild to subclinical disease. Unlike other important virus disease of cattle, bovine herpesvirus-1 and bovine virus diarrhea virus, abortion is not a direct result of BRSV infection. BRSV commonly occurs with secondary bacteria, as is often the case with other respiratory virus infections in cattle. Secondary bacterial infections usually result in more severe disease and a poorer prognosis.