A perspective on respiratory disease in feedlot cattle.

The etiological factors causing acute pneumonia in feedlot cattle are complex in terms of their interactions with the host to cause clinical disease or death. The most significant agent is Pasteurella hemolytica, but it may be acting relatively late in the overall sequence of events.It is necessary to develop an overall strategy to determine the pathogenesis of the disease in the field. Approaches to this objective are discussed, with the emphasis on the role of the epidemiologist.