This complex is manifested as one entity, bronchopneumonia . Yet, it can be caused by a variety of factors that interact to cause severe respiratory distress and possibly death. BRD in beef calves is called shipping fever, because the greatest incidence of bronchopneumonia occurs after shipment to stocker operations or feedlots. The main cause of BRD illness in calves is the tremendous exposure to infectious agents along with stress associated with weaning, commingling, and transportation. The clinical symptoms of BRD usually develop five to 14 days following management or environmental stresses.
Signs can be variable due to the many causative agents possibly involved in the disease complex.
Discovery of dead cattle and a high percentage of animals exhibiting depression and other signs of illness are not uncommon. Experimentally, the most common early symptom of BRD is appetite depression or anorexia and fever, so it is very important to diligently check and recheck newly stressed cattle for feed consumption. Tracking feed intake with records can be very beneficial. Cattle that have been off feed for over a day may appear gaunt. Early in the course of BRD the cattle may appear slightly depressed.