Response of the respiratory tract of calves kept at controlled climatic conditions to bovine Herpesvirus 1 in aerosol.

Seven experiments with four calves each were conducted in which the calves spent at least four days of adaptation in an environmental chamber and then were subjected to climatic stress in the form of a number of constant ambient temperature and humidity combinations. On the second day of climatic stress the calves were individually exposed to measured numbers of infectious units of bovine herpesvirus 1 (BHV1, virus of infectious bovine rhinotrachetis) in aerosol. The calves were killed seven or eight days later. Mycoplasma were found in some nasal swabs and in one lung. Certain bacteria but no Pasteurella were often isolated from the lungs. Bovine herpesvirus 1 was isolated from chamber air and from most postinoculation nasal swabs, tracheas and lungs. The number of macro- and microscopic lesions did not appear to be influenced by the climatic conditions of the experiments. The histopathological changes in epithelium at all levels of the respiratory tract were described in detail.