Bacterial Pneumonia in the Horse

Pneumonia refers to inflammation of the lungs. In horses, this is usually due to a bacterial infection, most commonly the streptococcal species.

Most horses get pneumonia by inhaling bacteria, which are often normal inhabitants of the upper airways. The lungs are usually able to clear the bacteria rapidly. However, if your horse has a depressed immune system, or has taken in an overwhelming dose of bacteria, then he may not be able to get rid of the bacteria, and pneumonia (lung infection) will develop.

There are many risk factors for bacterial pneumonia: those most important include a recent viral upper respiratory infection, moderate to severe exercise or overtraining, long-distance transport, overcrowded barns, and esophageal obstruction (choke).

What to Watch For



Home Care

Monitor your horse's rectal temperature once or twice a day. The horse's normal temperature ranges between around 99° F to 101° F. Also monitor your horse for any increase in coughing or nasal discharge. Note whether his appetite is good, and whether he looks bright and alert when you enter the barn.

Keep your horse in a temperate, well ventilated but draft-free environment. Avoid damp, poorly ventilated barns. Try to avoid dusty bedding, or moldy, dusty hay.

It is extremely important that you follow all instructions for antibiotic treatment. Your horse is likely to look and feel better long before the infection is completely cleared. If you stop antibiotic treatment too early, the infection will recur, and may be more difficult to cure the second time.

Give your horse plenty of time to recover if he has just undergone strenuous exercise – his immune system will be down. Whenever possible, don't tie your horse's head up when shipping, and avoid hay bags.

Have any horse with a cough or fever evaluated by your veterinarian; most horses will have a viral infection, but a few will go on to get pneumonia.

Pneumonia refers to inflammation and consolidation of the lungs. When areas of the lung that are normally filled with air become filled with inflammatory secretions like mucous and pus, this is called consolidation.

In horses, pneumonia is usually characterized by colonization and infection of the bronchioles, air sacs, and parenchyma by bacteria. Rarely, fungi and parasites may also cause pneumonia, as well.

The most commonly involved bacteria are streptococcus species that are gram positive, which refers to the type of cell wall. We often find a variety of gram negative bacteria, which are bacteria that have a thin cell wall and carry endotoxins as well.

The most common route of infection is inhalation (meaning that the horse breathes in the bacteria). Horses can also, less commonly, develop pneumonia through a primary infection in the blood.

Pneumonia in horses is generally not contagious; that is, there is no rapid spread from individual to individual. However, the same risk factors that apply to one horse in the barn may well apply to others, so occasionally you may have multiple horses with pneumonia.

Horses have a tremendous respiratory reserve, so pneumonia may be well established by the time you see signs such as an increased respiratory rate, cough, or fever. Severe heaves, a non-infectious cause of respiratory difficulty, may have many of the same signs as pneumonia, but the treatments are very different. It is important to pursue a diagnosis and treatment promptly so that your horse has the best chance of recovery.

Risk Factors

Veterinary care should include diagnostic tests and subsequent treatment recommendations



Your veterinarian will usually want to re-check your horse within the next few days, depending on how sick your horse is. At this time, he will listen to your horse's lung sounds, to determine if things are improving. He will probably also take another complete blood count, to see if the body's inflammatory response system is responding to the antibiotics.

The results of culture and sensitivity are usually available within 3 to 5 days. There is really no good way to make the results come back any faster – the laboratory is completely dependent upon how fast the bacteria grow in culture. If your horse is doing well, it frequently turns out that the empirical choice of antibiotics was correct. If your horse is not improving, or is not doing as well as you and your veterinarian might like, this is usually the time to change antibiotics.

Your veterinarian will usually continue with a given antibiotic for at least 48 hours before concluding that it is not working.

If your horse's pneumonia was severe enough that it required a visit or a stay at the hospital, you will probably be advised to bring your horse back for re-check x-rays at the time when you will be discontinuing antibiotics. This will enable your veterinarian to determine if there are any small vestiges of disease left.

After your veterinarian has pronounced your horse cured, remember that he has gone through a long and physically exhausting illness. It is important to give him plenty of rest (usually at least one month of pasture rest) before bringing him back into training.

When you do bring your horse back into training, do so gradually and slowly. It will take time to get back to the same level of fitness that he had prior to the pneumonia. Although most horses maintain their level of fitness for 4 to 6 weeks, recovery from pneumonia takes longer, so expect to spend 8 to 12 weeks getting your horse back into top condition.