They Don’t Call It "Heaves" Anymore
November 2007
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
Diet
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. We offer a Hay Steamer on this site.
Heaves
By: Lydia F. Gray, DVM, MA
SmartPak Staff Veterinarian and Medical Director
November 2007
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