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What are Rattles?

Pneumonia that is caused by the bacteria Rhodococcus equi (R equi) is also called rattles. The R equi bacteria lives in manure and is prevalent throughout where foals reside. Presenting with signs of a severe bronchitis, the infection must be treated quickly, or it may lead to large ulcers in the foal’s lungs and intestines and may be fatal. Also known as summer pneumonia, rattles is one of the five most common diseases of horses.

Pneumonia caused by the bacteria Rhodococcus equi is also known as rattles or summer pneumonia and is most often seen in foals from two months to six months old.

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Symptoms of Rattles in Horses

Should your foal develop rattles, you may notice the following symptoms:

  • Trouble breathing
  • Rattling sound when breathing
  • Appearing weak and lethargic
  • Showing no appetite
  • Fever
  • Diarrhea
  • Rapid pulse
  • Cough
  • Watery eyes
  • Pus-filled, thick discharge from his nose

Typically, rattles will start with increased bronchial sounds along with a cough. Over time the cough will turn into a wheeze. In one to two days your foal will develop a fever and an increased respiratory rate. Should your foal remain untreated, crackling sounds will evolve that can be heard throughout his lungs.


In most cases rattles is due to the bacteria R equi. It is thought that another bacterium, Streptococcus zooepidemicus, can also cause rattles, though these bacteria may be less toxic. The symptoms of pneumonia due to R equi are not really any different than those of other types of pneumonia.

Causes of Rattles in Horses

Typically, the cause of rattles is the R equi bacteria that can be found in horse manure. Foals between the ages of two and six months old are most likely to be affected and those that do not receive colostrum, live in an overcrowding situation or in a cold, damp environment are most susceptible to the condition. In breeding farms, the more the farm is contaminated with the R equi bacteria, the younger the foal will be when affected. Another bacteria, Streptococcus zooepidemicus, may cause rattles, though it is possibly not as toxic as R equi bacteria.

Diagnosis of Rattles in Horses

It is challenging to diagnose rattles in early stages. In many cases the foal will become extremely ill before it is noticed that something is very wrong. Even with a fever, the foal will continue to be alert and will still suckle on the mare. 

Should you notice symptoms in your foal, you will want to contact your veterinarian. Your veterinarian will conduct a full physical examination of your foal and ask you for information regarding the symptoms you noticed, when you first noticed them, and any changes that have occurred.

To diagnose rattles, your veterinarian will utilize CBC and serum chemistry testing, which will show anomalies that point to infection and inflammation. In rattles, neutrophilic leukocytosis and hyperfibrinogenemia are often seen and the extent of those can give insight into your foal’s prognosis. It is likely that your veterinarian will conduct radiographs of your foal’s lungs and look for perihilar alveolarization, consolidation and abscessation, as well as nodular lung lesions. Your veterinarian will seek to isolate the bacteria through a bacterial culture. It can then be tested to determine the type of bacteria causing the infection, and is required to confirm the diagnosis.

Treatment of Rattles in Horses

Treatment of rattles by antibiotics should be started as soon as possible. Once your veterinarian determines that your foal is suffering from rattles, he will start him on an antibiotic, which can be changed if necessary once culture and sensitivity tests come back. It has been found that R equi responds well to erythromycin and rifampin, which can be administered orally. The antibiotics will enter the phagocytic cells where the R equi bacteria are found.

Your foal will require the antibiotics throughout the time he shows symptoms and for a week after the veterinarian determines he is cured of the disease (as determined through x-rays or blood testing). The extended treatment is necessary as the bacteria will persist in abscesses in your foal’s lungs and rattles will often recur. Medications like gentamicin or trimethoprim-sulfamethoxazole are also able to treat the disease, however, must be administered through injection. Anti-inflammatory medication will likely be recommended to lower your foal’s fever and your veterinarian will treat him for dehydration.

Recovery of Rattles in Horses

Your foal should be kept in a warm and dry environment. It is important that you administer the antibiotics to your foal as recommended by your veterinarian and attend follow up appointments as necessary in order to ensure the best outcome for him. 

Making sure that foals get enough colostrum and are provided with a dry, clean environment with clean feed and bedding will help to prevent rattles. Following the vaccination and de-worming recommendations of your veterinarian will also help to keep your foal in good health, decreasing his susceptibility to the bacteria that cause pneumonia.