Respiratory tract reaction in young bovine animals and their significance

Understanding the pathogenesis of a disease is a prerequisite to developing measures to combat it. Most of the respiratory diseases affecting young bovine animals, indoors or outdoors, are considered to be due primarily to micro-organisms or parasites. However, not only have micro-organisms been isolated from the respiratory tracts of calves without clinical disease but striking morphological changes in the respiratory system, producing clinical disease, have not been linked with causal agents. A fundamental component of the pathogenesis of any disease is the morphological reactions involved in the affected system; these are the structural damage caused by the agent directly and the ensuing immunoinflammatory response accompanied by a repair reaction. The significance of some of these reactions and the difficulties associated with identifying and interpreting them will be considered here. The limited space precludes quoting many appropriate references.