“…A myriad of factors predispose cattle to this disease, including transportation, weaning, overcrowding, disrupted social structures, and other stressors in addition to precipitation, fluctuating environmental temperatures, and viral infection with bovine viral diarrhea virus, infectious bovine rhinotracheitis virus, bovine respiratory syncytial virus, and parainfluenza 3 virus (20). These factors are thought to compromise respiratory defenses, thus allowing opportunistic pathogens to proliferate, invade, and colonize the lung and incite the inflammatory reaction responsible for the clinical signs of the disease (54). The interactions between these multiple host, agent, and environmental factors are complex, and the importance of the innate pulmonary defense system and how stressors alter its function are the subject of current investigation.…”