Pneumonia in Dairy Cattle

Adapted by Dr. Pat Blanchard, California Animal Health and Food Safety Laboratory

Submissions to the California Animal Health and Food Safety Laboratory for respiratory infections in dairy cattle, particularly calves from 1 day to 5 months of age, increase during the fall and winter months. There are three main categories of lung infections seen in cattle.

1. Bronchopneumonia

Occurs from inhalation of bacteria or viruses into the lung. This type of pneumonia usually affects the front and lower parts of the lung. Bacteria, particularly Mannheimia, Pasteurella and Mycoplasma, are the most commonly found infectious agents in this type of pneumonia.  Other bacteria can also be found, including Histophilus, Arcanobacterium, Streptococcus and Bibersteinia, but they are less common. Outbreaks of this type of pneumonia that does not respond well to antibiotics may have a viral component.  Bovine respiratory syncytial virus (BRSV) is the most common virus found in pneumonia cases in calves. On occasion a dairy may experience an outbreak of IBR, but use of intranasal vaccines has reduced the frequency of finding this virus in calves.

On some dairies and calf ranches, calves will exhibit head tilts and droopy ears; this is due to infection of the middle ear with the same bacteria found in the lung of these calves. The bacteria can be found in the deep nasal cavity and spread from there to the lung and up the eustachian tubes to the middle ear as is common in children with repeated ear infections.  When the infections become chronic in the ear, the earlier bacteria like Mannheimia and Pasteurella disappear, and Mycoplasma bovis remains. The pus from the infection can eat away at the bone around the middle ear, causing permanent scarring and loss of hearing.  A study done at CAHFS Tulare a number of years ago found a high incidence of middle ear infections in calves with pneumonia where only a low percent were reported to have droopy ears or head tilts. This indicates that most middle ear infections clear up when the calf is being treated for pneumonia, but some persist and lead to clinical signs.

2. Interstitial pneumonia

Occurs most often due to Salmonella Dublin (aka Salmonella group D1 or S. Dublin). This bacteria spreads to the lung through the blood, so it affects all the lung lobes equally. The lung may fail to collapse, appear wet and heavy with small hemorrhages compared to bronchopneumonia, where part of the lung is hard (like liver) and sinks in water. Salmonella Dublin is a cattle-adapted Salmonella type, and adult cows can carry and shed it in their milk or feces. In addition, calves may harbor it in the intestine or lymph nodes, and when their colostral antibody drops between 1-3 months of age, the bacteria spreads to their lung, liver and spleen, causing disease. Typical calves with Salmonella Dublin are between 3 weeks to 4 months of age, have a fever, increased respiratory rate, may have difficulty breathing, decreased appetite, look depressed and may have diarrhea. These calves often have a history that they do not respond well to antibiotics. The poor response is because antibiotics used are often intended to treat pneumonia due to bacteria like Pasteurella or Mannheimia which are very sensitive to the antibiotic, whereas S. Dublin is not as sensitive, so the antibiotic does not maintain adequate levels in their blood long enough to kill the Salmonella.

3. Aspiration pneumonia

It is observed after a calf or cow inhaled fluid, feed or milk into their lung. This can occur from a misplaced esophageal feeding tube used to provide calves with milk, colostrum or electrolytes. Also, when calves are very weak from diarrhea or a prolonged birthing, they may have a poor swallow reflex, so fluids placed in their mouth (milk or colostrum) may accidentally enter the trachea, settling in the lung. A number of calves with aspiration pneumonia may have only one side of the lung affected, and this suggests they were lying down perhaps on one side when the aspiration occurred so the foreign material settled in the lower lung. In cows, aspiration can occur when they are intubated for treatment of metabolic or digestive problems, and we also rarely see cows that have aspirated rumen contents into their lungs during a roll and tack procedure to correct a displaced abomasum. If calves display signs of pneumonia in the first few days of life or shortly after being intubated, aspiration pneumonia should be suspected. The bacteria found in these lungs are the common ones found in the environment like coliforms, streptococcus and like environmental mastitis are not considered infectious but rather opportunistic infections.

Selecting the best antibiotic to treat a bronchopneumonia, particularly when the one of choice does not seem to be working, requires taking samples from untreated calves early in the infection before secondary bacteria move in. Having your veterinarian sample the deep nasal cavity via a guarded deep nasal swab can be a valuable means to determine which bacteria may be causing the pneumonia. A second swab can also be used to screen for IBR, BVDV, BRSV and bovine coronavirus by PCR method. Bovine coronavirus testing, however, does not distinguish the respiratory virus from the common diarrhea strain. Unguarded nasal swabs often result in overgrowth, the normal bacteria found in the front of the nose making it very difficult to identify important pneumonia causing bacteria. Interstitial pneumonia associated with Salmonella Dublin often results in the death of some calves so submission of dead calves or lung and other tissues from dead calves, can also be valuable to determine what might be causing the pneumonia signs. However, dead calves with bronchopneumonia that have been sick and treated for a long time often do not provide the information desired, as they will have scarred lungs with abscesses, so the bacteria and viruses that started the pneumonia are no longer present.

Working with your veterinarian to select appropriate animals for testing is a valuable means to ensure the causative agents are identified so appropriate treatments and vaccinations are used to prevent and resolve pneumonia outbreaks.

Breakdown of common agents found in 130 pneumonia cases from Oct-Dec 2011

Link to PDF Version: Pneumonia in Dairy Cattle