The following article by Dr. John Maas, Extension Veterinarian at UC Davis, provides a good summary of a cattle health problem many producers can or have experienced - pneumonia in cattle. This can be a common and sometimes frustrating problem. Use of antibiotics to treat these cattle is just as common and sometimes just as frustrating.
Most producers think of pneumonia as a single condition, because of the symptom syndrome.
Peumonia, however, has several different causes and varies in severity from mild to rapidly fatal, and we know from experience the disease can be unpredictable. Pneumonia is an inflammation of the tissues of the lungs that results from the response of the animal to an infectious agent, which can be either a virus or a bacteria, or in many cases both. Often the virus infection causes tissue damage, and then bacteria invade the compromised tissues. The bacteria most often involved include Pasteurella hemolytica and Pasteurella multocida. These two bacteria are never far from cattle and are particularly adept at infecting lung tissue damaged by viruses.