The term “stable cough” refers to a syndrome where horses start coughing when they’re confined to a barn. The problem isn’t related to respiratory infections, although it does put the horse at a higher risk of developing one. Nasal discharges due to stable cough are more thin or frothy, as opposed to the thick, discolored discharges associated with an actual infection. The stable cough is dry and hacking.
More significant than the cough is why the horse coughs. The cough is caused by airway spasm and inflammation called recurrent airway obstruction (RAO). The terms “heaves” and “stable cough” may be used interchangeably or heaves reserved for the most severe cases. Once irreversible injury to the lungs has occurred, the changes begin to resemble chronic obstructive pulmonary disease in people (COPD).
The most common trigger of RAO is mold found in straw and hay. Even hay and straw that looks clean and smells sweet may contain some level of mold. Environmental molds growing on untreated wood or concrete areas may also contribute. Although this sounds like an allergy, a Swiss study found no increase in IgE, the allergy immunoglobin, in lung tissue samples from horses with RAO. Other studies have found increased levels of IgE specific for common molds.
All the studies describe increased numbers of mast cells, which can release histamine and are involved in tissue remodeling and scarring, as well as infiltration with lymphocytes and neutrophils suggesting that RAO is primarily an inflammatory problem. The airway irritation in RAO can also be worsened by ammonia from decomposing urine, dust/mites and any small particles suspending in the air.
Some people dismiss stable cough as a minor problem, as long as the horse isn’t running a fever or acting sick. This is a mistake. Left uncorrected, RAO will progressively worsen and eventually cause permanent lung damage. RAO also has been found to predispose high performance horses to lung bleeding - EIPH (exercise induced pulmonary hemorrhage).
What To Do
• Fresh air: Whenever possible, horses with stable cough/RAO should be kept outside. Removing exposure to the offending irritants is by far the most effective treatment. Healthy horses tolerate cold well and will remain comfortable as long as they have ready access to shelter.
If they must be stabled, it’s imperative to not close the barn up and make sure there is a constant flow of air through the barn. Opening windows above head level of the horses and doors locate at the ends of aisles will keep air moving without subjecting the horses to direct drafts. If the barn isn’t well ventilated, consult a contractor for how best to correct this.
• Bedding: Straw might not be the best choice here, due to its natural dust and molds. Shavings are better, but the aromatic oils may bother some horses, and these are sometimes infested with mold as well. Kiln-dried, low-dust shavings cost more but can make a big difference. You might also consider a pelleted or cardboard-based bedding.
It doesn’t do any good to only replace bedding of the coughing horse. All stalls have to be treated the same way. When using pelleted products, be sure to follow directions for wetting them slightly to rehydrate, and if you run across bags with large amounts of fine, dusty materials return them for a refund. These products are too expensive to settle for less than precisely what you need.
• Diet: For mildly affected horses, or when the problem is excessive dust rather than molds, thoroughly wetting/dunking the hay before feeding it may do the trick. However, it’s usually not enough. Cubed or pelleted hays are a better choice, since the grasses used in these are typically harvested at a higher level of moisture then cut and heat dried before processing. Pelleted complete feeds also work well for many horses. Grains can harbor their own assortment of molds and are problematic for some horses. In that case, switching to a pelleted, beet-pulp-based and grain-free feed or soaked beet pulp alone will help.
• Antioxidant Supplements: Several studies have consistently shown reduced levels of antioxidant nutrients in the lungs of horses with RAO. A 2002 study from Belgium found that supplementing horses with vitamin C, vitamin E and selenium was effective in improving the levels of these antioxidants, as well as glutathione, and improved exercise tolerance and inflammation in the lung. In fact, one of the reasons these horses do so much better on pasture may be the presence of natural antioxidant vitamins and omega-3 fatty acids in live grasses.
• Other Supplements: Spirulina, at 20 grams twice a day, may be helpful as a natural antihistamine and for immune system moderation (see December 2004). We’ve also found work of breathing is eased, exercise capacity increased and recovery times improved with a blend of Chinese herbs. Human studies have found that airways are often hyper-responsive with magnesium deficiency and that treating with magnesium can help them open up again, but this treatment may only work when given intravenously or as an aerosol. Magnesium effects haven’t been studied in horses.
• Vicks: Not too exciting, but plain old Vicks VapoRub or a generic equivalent applied liberally below the nostrils or used in a nebulizer or vaporizer effectively relieves airway spasm/irritation and thins mucus so that it is more easily eliminated from the respiratory tract.
• Drugs: A wide variety of bronchodilating, antihistamine and corticosteroid drugs are available for use orally, by injection or by inhalation. However, attempting to control RAO with drugs only is like trying to treat a chemical burn without removing the chemical from the skin.
For many horses, all that is required to fix the problem is to get them outside. Don’t consider using drugs until all the other sugested approaches have been exhausted.
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