Inflammatory Airway Disease in Horses – IT’S MORE THAN JUST A COUGH
FOR MANY HORSE OWNERS, hearing a small, occasional cough when their animal first starts to work does not seem like a big deal. But performance horse owners realize that low grade inflammation in the lower respiratory tract can cause trouble long before obvious clinical signs are apparent. A mild cough with a little mucous discharge might mean only a slight irritation that would respond to a few days of rest — but it might also be a sign of more serious trouble.
Coughing is not normal if it shows up consistently at the beginning of exercise, occurs spontaneously in the barn or during feeding, is deep or productive, or reduces performance in any way. A persistent cough that lasts longer than four weeks is likely a sign of inflammatory airway disease (IAD). Other signs of IAD that may occur less consistently include fading at the end of a race, moving the jaws or swallowing after a cough, and reluctance to collect or flex at the poll. IAD should also be considered when horses show increasing reluctance to work for no obvious reason.
WHAT CAUSES IAD?
The specific cause is not known. It is most likely the result of multiple insults. Performance horses are subjected to many irritants in barns, trailers, dusty warm-up pens and arenas. Research in humans has proven that the inhalation of particles less than 10 micrometers in size will cause inflammation of the airways. Specific research on particle size in horses has not been done, but signs of inflammation like visible mucus are associated with particles between 0.7 and 2 micrometers in diameter.
Rodeo arena dust is one of the most irritating substances a horse can be exposed to. Barrel racing horses have increased risk of exposure because of the large quantities of dirt thrown into the air from the combination of high speed, stopping and turning. The smaller dust particles will remain suspended in the air, especially right next to the barrels. Horses that run the barrel pattern after multiple horses have already run it are more at risk than those that run immediately after the ground is worked by a tractor.
Horses that travel to compete face the constant challenge of viruses and bacteria. It can be difficult to determine whether a horse has IAD or a low grade primary infection caused by a virus or bacteria, since the symptom patterns can be very similar. Whereas viruses are rarely identified in transtracheal wash samples, bacteria commonly are; but again, in either case – viral or bacteria – we have no way of knowing whether those pathogens might have caused the inflammation or are present because of the inflammation.
Antibiotics are often prescribed based on the culture and sensitivity results for the bacteria found in the transtracheal wash sample. It is then not uncommon for subsequent samples to reveal the presence of an entirely new bacterial infection. From a holistic viewpoint, this would suggest that bacteria are present because of the inflammation rather than the other way around, in which case the focus should be on decreasing the inflammation instead of treating an infection.
Treatment of inflammatory airway disease is focused on management to decrease exposure to irritants, and reversing the bronchoconstriction caused by the release of inflammatory mediators in the lower airways.
1. BEDDING AND DUST CONTROL
The type of bedding is important. Shavings and straw are easily broken down into small particles when horses continually walk on them. These types of bedding will also harbor molds unless all moist materials are removed frequently.
Washed river sand can be a better choice for bedding as it does not break down as easily when walked on. Sand can also be misted with water to keep the dust down with less fear of mold formation. Care must be taken to remove all manure and urine-soaked sand every day, and fresh sand should be brought in as needed.
Keep all bedding in the horse’s stall and trailer clean and fresh in order to avoid mold and ammonia fumes. Fine particles of manure can be very irritating when inhaled. Hay should be fed on the ground or in low mangers that are cleaned out regularly. Trailers with feed mangers will not allow the horse to lower his head to clear his respiratory passages. If the horse is to be tied in the trailer, make sure the rope is long enough to allow the top of the head to drop below the withers.
Dust control in the arena and barn can be achieved with frequent watering. Wet the barn aisles down before sweeping or blowing. High ceilings and good ventilation will help drop the concentration of fine dust particles in the air. Avoid turning on fans when stalls are being cleaned or when traffic in the barn is heavy. Never store hay above the stall area; a separate building for hay storage is ideal. Regular turnout in the pasture will allow the horse to get his head down and have a break from a dusty barn.
When possible, horses should not be stabled in the same barn as an arena. At shows or rodeos, the horse should be kept outside as much as possible. Horses should not be schooled or warmed up in crowded arenas if it can be avoided.
2. BODYWORK CAN HELP WITH BREATHING
Horses must be able to breathe deeply to clear their lungs. If a patient is very muscle sore or has a fixated rib, he may be breathing shallowly. In the absence of deep breathing, the horse may be unable to clear mucous and inhaled debris from the deeper airways, setting up the potential for bronchial infection and inflammation. Regular bodywork such as chiropractic, TTouch, massage or acupressure will allow detection and correction of these problems so that free breathing can be restored quickly.
3. MEDICATIONS – PROS AND CONS
Antihistamines are rarely effective in treating IAD, despite the fact that histamine is the predominant mediator produced by mast cells and a secondary mediator produced by neutrophils. Histamine triggers bronchoconstriction, and bronchodilators may give temporary relief but do not address the underlying inflammation. The response to bronchodilators tends to decrease the longer they are used.
Corticosteroids are the Western treatment of choice and some horses will temporarily respond well to them. Horses with a hyper-reactive airway produce more mast cells and do not respond to steroids. Steroids are palliative at best and suppress the immune system, making the horse even more susceptible to infection. Side effects of steroids also include gastrointestinal bleeding and organ damage.
4. NUTRITION AND SUPPLEMENTS
Nutritional support and natural products such as herbs can be utilized to prevent and treat IAD.
• Omega-3 fatty acids have anti-inflammatory action that is often more effective than drugs. Mast cell mediated inflammation responds well to Omega-3 fatty acids. Flax seeds, chia seeds and blue green algae are good sources.
• Probiotics can be added to the diet and support the immune system by enhancing the function of the digestive system.
• Noni and mangosteen fruit contain natural antioxidant and anti-inflammatory substances that help combat inflammation.
• In general, herbs can be very helpful in supporting the respiratory tract. Decongestant herbs like ephedra help clear excess mucous by dilating the brochiolas. Be aware that this herb may test positive so it should not be used during competition. This herb should not be used without the guidance of an experienced herbalist. Safe, nutritional herbs such as marshmallow, slippery elm, comfrey, mullein, and fenugreek help thin and clear out mucous. Lobelia is an antispasmodic that can relax bronchospasms. This is a very strong herb and should not be used without the guidance of an experienced herbalist.
• Pure, whole particle beta glucan helps with inflammation by mobilizing white blood cells to areas of injury or inflammation. These white blood cells (macrophages) then remove damaged tissue quickly before it has time to trigger more inflammation. Beta glucan is considered an immune modulator, so it can dampen an overactive immune response. Medicinal mushrooms such as cordyceps contain multiple forms of beta glucan.
• Occasionally, a certain farm will have a high incidence of IAD, which can be due to many factors including environmental irritants or resident viral, bacterial or fungal pathogens. If this situation develops, and healthy horses introduced to the farm develop symptoms, it may be valuable to make a homeopathic nosode to be given to all horses on the farm, and all new horses as they are brought in. To do this, samples from a transtracheal wash are sent on ice immediately to a homeopathic pharmacy where a remedy is made based on homeopathic principles. While most homeopathy is based on individual prescribing, a high percentage of horses can respond to homeopathic action that is specific to the pathogen on a particular farm.
• Antibiotics, steroids and/or bronchodilators can be used for short term treatment, but they are rarely curative. Rest, in combination with herbal decongestants and anti-spasmodics, can be used in place of conventional drugs.
DIAGNOSING THE PROBLEM
Diagnosis of IAD is based on a combination of clinical signs, the results of an endoscopic exam, transtracheal and bronchoaveolar lavage (BAL) results, and the horse’s response to treatment. It is important to determine the type of inflammatory cells recovered in the lavage fluid. When neutrophils are found as the predominant cell type, there is a better prognosis for treatment because this type of inflammation does respond to steroids and other anti-inflammatory medications. Quarter horses, as a breed, are more likely to produce mast cells as a response to organic matter suspended in rodeo arena dust. Barrel racing horses that respond to irritation with mast cell cytosis do not respond to corticosteroid anti-inflammatory therapy and are more difficult to treat successfully.