Sudden dietary changes, weaning, cold, drafts, dampness, dust,
high levels of ammonia, poor ventilation in general, and the
mixing of widely divergent age groups all play a role in
respiratory disease in groups of animals. Stress and mixing of
animals from several sources should be avoided or minimized.
Establishing individual animal identification, making accurate
clinical and postmortem diagnoses, and maintaining a record
system of diagnosis and treatment are important to minimize or
control outbreaks of pneumonia. Transportation over long
distances is another stress factor that plays a major role in
the pathogenesis of respiratory infections in large animals.
Immunization can help control respiratory infection. However,
control may be compromised by improper timing, use of
ineffective or inappropriate vaccines, or overwhelmingly
negative management practices. In most cases, severe insults to
the natural defenses cannot be reversed later by therapeutic
agents and biologicals. The mucosal surfaces of the res