obsolete bovine respiratory disease complex true DOID:3732 A pneumonia which has a multifactorial etiology and develops as a result of complex interactions between environmental factors, host factors, and pathogens leading to pulmonary lesions caused by various micro organisms ( essentially viruses and bacteria). Environmental factors (eg, weaning, transport, commingling, crowding, and inadequate ventilation) serve as stressors that adversely affect the immune and nonimmune defense mechanisms of the host. In addition, certain environmental factors (eg, crowding and inadequate ventilation) can enhance the transmission of infectious agents among animals. disease_ontology