September 2023 Issue

Page 40 September 2023 EAST COAST EQUESTRIAN Rise in Smoke and Smog Leads to More Equine Asthma forest-fire smoke is another seri- ous contributor to air pollution. Smog causes the lung inflam- mation associated with mEA. Therefore, it is also likely that air pollution from engines and from forest fires will also trigger asth- ma attacks in horses with sEA. Smog and smoke contain many harmful particulates and gasses, but very importantly they also contain fine particulate matter, known as PM2.5. The 2.5 refers to the diameter of the particle being 2.5 microns. That’s roughly 30 times smaller than the diam- eter of a human hair. Because it is so small, this fine particulate is inhaled deeply into the lungs where it crosses over into the blood stream. So, not only does PM2.5 cause lung disease, but it also causes inflammation elsewhere in the body including the heart. Worldwide, even short- term exposure is associated with an increased risk of premature death from heart disease, stroke, and lung cancer. This PM2.5 stuff is not trivial! In horses, we know that PM2.5 causes mEA, so it’s logical that smog and forest-fire smoke exposure should cause exacerba- tion of asthma in horses, but we don’t know about heart disease or risk of premature death. Symptoms, Diagnostic Tests, and Treatments Equine asthma manifests with a spectrum of symptoms that vary in severity and degree of de- bilitation they cause. Just like in people with asthma, the airways of horses with mEA and sEA are “hyperreactive”. This means that the asthmatic horse’s airways are extra sensitive to barn dusts that another horse’s lungs would just “ignore”. The asthmatic horse’s airways constrict in response to these dusts, making it harder to get air in and out of the lungs. In horses with mEA the narrowing is mild. In horses with sEA the constriction is extreme and is the reason why they develop the “heaves line” – they have to use their abdominal muscles to help squeeze their lungs to force the air back out of their narrow air- ways. They also develop flaring of their nostrils at rest to make their upper airway wider to get more air in. Horses with mEA do not develop a heaves line, but the airway narrowing and inflam- mation do cause reduced athletic ability. The major signs of mEA are coughing during or just after ex- ercise that has been going on for at least a month, and decreased athletic performance. In some cases, there may also be white or watery nasal discharge particular- ly after exercise. Often, the signs of mEA are subtle and require a very astute owner, trainer, groom, or rider to recognize them. Another very obvious fea- ture of horses with sEA is their persistent hacking cough, which worsens in dusty conditions. The cough develops because of airway hyperreactivity and be- cause of inflammation and excess mucus in the airways. Mucus is the normal response of the lung to the presence of inhaled tiny particles or other irritants. Mucus traps these noxious substances so they can be coughed out, which protects the lung. But if an asthma-prone horse is constantly exposed to a dusty environment it leads to chronic inflammation and mucus accumulation, and the development or worsening of asthma – along with that charac- teristic cough. Accurately Diagnosing Equine Asthma Veterinarians use a combi- nation of the information you tell them, their observation of the horse and the barn, and a careful physical and respiratory examination that often involves “rebreathing”. This is a technique where a bag is briefly placed over the horse’s nose causing them to breathe more frequently and more deeply to make their lung sounds louder. This helps your veterinarian hear subtle changes in air movement through the lungs and amplifies the wheez- es and crackles that characterize a horse experiencing a severe asthma attack. Wheezes indicate air “whis- tling” through constricted airways, and crackles mean airway fluid buildup. The fluid accumulation is caused by airway inflammation and contributes to the challenge of getting air into the lung. Other tests your veterinar- ian might use are endoscopy, bronchoalveolar lavage, and in the specialist setting, pulmonary function testing. They will also perform a complete blood count and biochemical profile assay to help rule out the presence of an infectious disease. Endoscopy allows your vet- erinarian to see the mucus in the trachea and large airways of the lung. It also lets them see whether there are physical changes to the shape of the airways, which can be seen in horses with sEA. Bronchoalveolar lavage, or “lung wash” is how your veteri- narian assesses whether there is an accumulation of mucus and inflammatory cells in the smallest airways that are too deep in the lung to be seen using the endo- scope. Examining lung wash fluid is a very important way to differentiate between the different types of mEA, between sEA in remission and an active asthma attack, and conditions like pneu- monia or a viral lung infection. Finally, if your veterinarian is from a specialty practice or a veterinary teaching hospital, they might also perform pulmonary function testing. This allows your veterinarian to determine if your horse’s lungs have hyperreactive airways (the hallmark of asthma), lung stiffening, and a reduced ability to breathe properly. Results from these tests are crucial to understanding the severity and prognosis of the condition. As noted earlier, mEA can go away on its own but medical intervention may speed healing and return to athletic per- formance. With sEA, remission from an asthmatic flare is the best we can achieve. As the disease gets worse over time, eventually the affected horse may need to be euthanized. Management, Treatment, and Prevention Successful treatment of mEA and sEA flares, as well as long- term management, requires a multi-pronged approach and strict adherence to your veterinarian’s recommendations. Rest is important because forcing your horse to exercise when they are in an asthma attack further damages the lung and im- pedes healing. To help avoid lung damage when smog or forest-fire smoke is high, a very useful tool is your local, online, air quality index (just search on the name of your closest city or town and “AQI”). Available worldwide, the AQI gives advice on how much activity is appropriate for people with lung and heart con- ditions, which are easily applied to your horse. For example, if your horse has sEA and if the AQI guidelines say that asthmatic people should limit their activity, then do the same for your horse. If the AQI says that the air quality is bad enough that even healthy people should avoid physical activity, then do the same for you AND your horse. During times of poor air quality (Image 2), it is recommended to monitor the AQI forecast and plan to bring horses into the barn when the AQI is high and to turn them out once the AQI has improved. Prevent dusty air. Think of running your finger along your tack box – whatever comes away on your finger is what your horse is breathing in. Reducing dust is critical to preventing the development of mEA and sEA, and for managing the horse in an asthmatic flare. Logical daily practices to help reduce dust exposure include: • turning out all horses before stall cleaning • wetting down the aisle prior to sweeping • never sweeping debris into your horse’s stall • using low-dust bedding like wood shavings or dust-ex- tracted straw products – which should also be dampened down with water • reducing arena, paddock, and track dust with watering and maintenance • when selecting footing substrate, consider low dust materials. • steaming (per the ma- chine’s instructions) or soaking hay (15-30 minutes and then draining, but never storing steamed or soaked hay!) • feeding hay from the ground or using hay feeders that sit on the ground • feeding other low-dust feeds • avoiding hay feeding systems that allow the horse to put their nose into the middle of dry hay – this creates a “nosebag” of dust Other critical factors include ensuring that the temperature, humidity and ventilation of your barn are seasonally optimized. Horses prefer a temperature be- tween 10-24 ºC (50-75 ºF), ideal barn humidity is between 60-70%. Optimal air exchange in sum- mer is 142 L/s (300 cubic feet/ minute). Winter air exchange of 12-19 L/s (25-40 cubic feet/min- ute) is ideal. In winter, needing to strip down to a single layer to do chores implies that your barn is not adequately ventilated for your horse’s optimal health. Comfort- able for people is often too hot and too musty for your horse! Medical interventions for controlling asthma are numerous. If your veterinarian chooses to per- form a lung wash, they will tailor the drug therapy of your asthmatic horse to the results of the wash fluid examination. Most veterinar- ians will prescribe bronchodilators to alleviate airway constriction. They will also recommend aero- solized, nebulized, or systemic drugs (usually a corticosteroid, an immunomodulatory drug like in- terferon-α, or a mast cell stabilizer like cromolyn sodium) to manage the underlying inflammation. They may also suggest nebulizing with sterile saline to help loosen airway mucus and may suggest feed additives like omega 3 fatty acids, which may have beneficial effects on airway inflammation. New Research and Future Directions Ongoing research is para- mount to expanding our knowl- edge of what causes equine asthma and exploring innovative medical solutions. Scientists are actively investigating the effects of smog and barn dusts on the lungs of horses. They are also working to identify new targeted thera- pies, immunotherapies, and other treatment modalities to improve outcomes for affected horses. Conclusions Both mild and severe equine asthma are caused and triggered by the same air pollutants, high- lighting the need for careful barn management. The alarming rise in air pollution levels poses an addi- tional threat to equine respiratory health. Recognizing everyday coughs as potential warning signs and implementing proper diagnos- tic tests, day-to-day management practices and medical therapies are crucial in combating equine asthma. By prioritizing the pro- tection of our horse’s respiratory health and staying informed about the latest research, we can ensure the well-being of our equine com- panions for years to come. 1. Work to prevent dust and to optimize barn air exchange 2. Avoid idling farm equip- ment and trucks around horses 3. Don’t ignore a cough – call your veterinarian 4. Monitor your local air quality index – it’s a free and simple way to help prevent lung damage! (Continued from page 22)