EN
Serological investigation of 185 serum samples of healthy cattle and 428 serum samples taken from cattle witih symptoms of respiratory diseases showed antibodies aigainst parainfluenza-3 (PI-3) virus, infectious bovine rhinotracheitis (IBR) virus, virus diarrhoea-mucosal disease (VDMD) virus, and adenovirus. The main causative agent of virus respiratory infections proved to be PI-3 virus. The remaining viruses were accompanying factors. The results of these investigations were confirmed by 135 virus isolaitions from nasal swabs taken from diseased cattle.