They Don’t Call It "Heaves" Anymore

By: Dr. Lydia Gray

At the International Workshop on Equine Chronic Airway Disease in 2000, a group of investigators eliminated the term COPD (chronic obstructive pulmonary disease) in favor of RAO (recurrent airway obstruction). This was done to indicate that this respiratory condition is not the same in horses as it is in humans.

RAO is defined as episodes of obstructive lower airway disease triggered by exposure to hay and bedding and characterized by difficulty breathing, severe airway inflammation, a large number of neutrophils (white blood cells), airway hyper-reactivity, and reversibility with bronchodilator treatment.

It typically develops in horses seven years of age or older that have spent a considerable period of their lives in a stable where they are fed hay. The signs of RAO include:
  • Coughing (including coughing up mucus)
  • Labored breathing
  • Flared nostrils at rest
  • Nasal discharge
  • Depression
  • Elevated respiratory rate at rest
  • Exercise intolerance or poor performance
  • Increased movement of abdomen during breathing (causing a "heave line")
RAO can usually be diagnosed based on the history and physical examination, although additional tests may be needed to rule out other conditions or to follow the horse’s response to treatment. These tests may include complete blood count (CBC) and routine chemistry, blood gas measurement, endoscopy, chest x-rays, bronchoalveolar lavage (BAL), lung biopsy and lung function tests.

While there is no cure for RAO, it can be successfully managed by reducing the horse’s exposure to organic dust and treating episodes of airway obstruction. This involves a four-pronged approach: 1) diet, 2) environment, 3) prescription medications and 4) supplements.

The single most important thing an owner can do is remove hay completely from the diet and replace it with another source of fiber. If this is not practical, then hay should be soaked for two hours before feeding. The next most important management change is to keep the horse outside 24/7. If this, too, is not practical, then the horse should be turned out as much as possible, especially when stalls are being cleaned or aisles are being swept. If the horse must be kept in a stall, straw should not be used for bedding. Instead, specially treated wood shavings, shredded paper or cardboard, peat moss, or other low-dust material should be used.

At this time, two categories of prescription medications are used to manage episodes of RAO: corticosteroids, which reduce airway inflammation, and bronchodilators, which relieve airway obstruction. Corticosteroids include dexamethasone and prednisolone or the newer beclomethasone or fluticasone. The most common bronchodilators used are in the beta-adrenergic agonist family and include clenbuterol and albuterol. While some of these medications can be given intravenously, intramuscularly, or orally, some can be given via specially made equine inhalers. This method deposits the medication exactly where it is needed, and avoids the side effects seen when medications must travel through the GI system or bloodstream to get to the site of action.

Research is ongoing as to the benefit of supplements in horses with RAO. University of Vienna researchers reported that a botanical preparation combining the extracts of several medicinal herbs seemed to be beneficial to horses with "heaves." In addition, RAO may place horses under oxidative stress, so antioxidant supplementation may be helpful to these horses. Supplementation with Vitamin C (ascorbic acid) in particular is being investigated for its role in neutralizing these reactive oxygen species.

Other Management Suggestions

Dust in hay is one of the worst offenders to a horse with "heaves," so replacing hay with another fiber source such as a complete feed is often recommended. Steamed or soaked hay or hay cubes are other alternatives.

About Dr. Lydia Gray

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