Managing Horses With Asthma
The latest on managing horses with equine asthma
It’s something that can be easy to forget. We neither inspect it daily for injuries or inconsistencies, as we do our horse’s body, nor do we watch it closely for subtle irregularities, as we do his gait. But it—the horse’s respiratory health—is vital. For our horses to thrive, much less be athletes, it must function properly, pumping massive amounts of air in and out of the body effortlessly.
A healthy horse at rest takes 10 to 14 breaths per minute, inhaling upwards of 150 liters of air in that time. But a horse diagnosed with asthma, just like his human counterpart, coughs, wheezes, and struggles to breathe. Airway inflammation and mucus accumulation associated with this condition make efficient performance nearly impossible for these horses.
Historically, we’ve known equine asthma better as inflammatory airway disease (IAD) and recurrent airway obstruction (RAO, or heaves), conditions that affect 25-80% of stabled horses in the United States, according to a 2006 paper by Tufts University’s Melissa Mazan, DVM, Dipl. ACVIM, and Andrew Hoffman, DVM, DVSc.
Since that paper was published, our perception of IAD and RAO has changed greatly. Because both of these diseases are characterized by airway inflammation and mucus accumulation, scientists are now labeling them equine asthma. A group of equine internal medicine specialists led by Laurent Couëtil, DVM, PhD, the section head of Large Animal Internal Medicine at Purdue University, in West Lafayette, Indiana, released a new consensus statement on the disease earlier this year (see TheHorse.com/37664).
While a diagnosis of equine asthma can be devastating, there are many ways horse owners can help their animals, especially through management and environmental changes.
While both inflammatory airway disease (IAD) and recurrent airway obstruction (RAO) now fall under “equine asthma,” there are still some important differences between them.
|Horses Most Affected||Younger competition horses||Mature horses, average age of onset is 9 years|
|Diagnosis||Difficult to detect upon physical examination, mild to moderate excess mucus seen on airway endoscopy after exercise||Abnormal lung function, which can be measured even at rest, and marked excess mucus seen on airway endoscopy|
|Effects on Performance||Causes exercise intolerance at maximum performance, but affected animals can still become top competition horses||Horses have trouble breathing even at rest; unlikely to become top athletes|
|Clinical Signs at Rest||No respiratory difficulties at rest, occasional coughing||Wheezing, frequent coughing, flared nostrils, labored breathing and abnormal lung function in horses challenged by environmental factors at rest|
The Root of the Problem: Air Quality
Stables are full of tiny particulates that can infiltrate the equine respiratory system. Culprits include ammonia from urine; mold and fungi from hay, straw, sawdust, and shavings; dust from indoor arenas, rain, hay, and bedding; endotoxins from manure; and dander and hair from stablemates and companion animals.
“Organic dust exposure has been shown to result in long-term declines in respiratory function and increased prevalence of chronic lung diseases in humans—it is logical to expect that the same exposures will have similar effects on equine respiratory health,” says Mazan.
Dust particles, which can contain microorganisms such as bacteria and molds, and noxious compounds such as ammonia and toxins, exacerbate IAD and RAO, says Emmanuelle van Erck–Westergren, DVM, PhD, Dipl. ECEIM, founder and owner of Equine Sports Medicine Practice, a referral center in Waterloo, Belgium.
It’s difficult to visually assess barn air quality, though, because you’re dealing with microscopic particles, she says. All barns have some level of dust that can be inhaled, but the number, particulate composition, and size dictate whether or not they are harmful to horses (and people). Particles can reach the upper airways (which extend from the nostrils to the throat), trachea, and lower airways, (which include the lungs and the bronchi that supply them), and some are even small enough to dissipate throughout the body via the bloodstream.
Mazan says owners can rent air assessment equipment to check their stables. Some rental companies also analyze collected air samples. She says testing costs between $500 and $5,000, depending on the scope. If you don’t want to rent equipment, you can hire an environmental testing agency to do the analysis for you.
Research over the years has shown that a variety of environmental factors can cause horses to develop equine asthma. These include, among others:
- Seasonal weather patterns;
- Proximity to roadways;
- Barn temperature and humidity;
- The number of horses being housed;
- Activity level within the barn;
- Ventilation and air flow;
- Stable configuration, including size, orientation, materials used in its design;
- Accumulation of mold- and dust-collecting items;
- Forage and bedding harvest and storage;
- Disinfection practices;
- Stall cleaning methods; and
- Raking, sweeping, and use of equipment such as blowers.
If horses with equine asthma are kept in strictly controlled environments, van Erck-Westergren says they can enter into a state of symptom-free clinical remission and be maintained that way. “Therapy is based on first eliminating the trigger factors in the environment,” she says. “It is utopian to think the disease can be solved without proper initial environmental changes.”
One of the first changes you can make involves your horse’s dietary forage. “The worst culprit is what they are eating,” says Mazan.
Researchers have shown a positive correlation between hay particulate inhalation and upper- and lower-airway mucus production. For this reason, Mazan advises against using traditional woven haynets: “Research shows that haynets encourage horses to bury their noses in hay, which exposes them to a higher particulate load.”
In a 2014 study Kathleen Ivester, DVM, a post-doctoral research assistant at Purdue University’s College of Veterinary Medicine, and colleagues performed bronchoalveolar lavage fluid (BALF) cytology on 49 Thoroughbred racehorses 12 to 36 months of age to measure their exposure to particulates, endotoxins, and ammonia 14 days and 28 days after beginning race training.
Sixteen horses consumed hay from haynets, and 33 ate hay on the ground. The haynet-fed horses were exposed to significantly higher levels of respirable particulates and endotoxins than the ground-fed group. This resulted in higher BALF eosinophil—a type of white blood cell—concentrations over time, which indicate pulmonary (lung) inflammation and potential hypersensitivity to inhaled allergens.
If you feed hay, van Erck-Westergren recommends steaming or soaking it before offering it to your horse, with one caveat: “Soaking the hay (longer than) 30 minutes promotes bacterial growth and can cause digestive problems,” she says.
Couëtil advises against feeding asthmatic horses a dry hay diet and instead recommends turning them out on grass pasture and feeding a complete pelleted feed. (Note that some of these horses should not be turned out on pasture.)
To reduce clinical signs, he also recommends supplementing these horses with omega-3 polyunsaturated fatty acids (PUFA) for at least five weeks and for as long as needed depending on exposure risk. His recommendations are based on his 2015 study with Nora Nogradi, DVM, MS, Dipl. ACVIM, of the Dubai Equine Hospital.
In the study they gave 43 horses either 30 g or 60 g of the PUFA docosahexaenoic acid (DHA) or 30 g of a placebo for eight weeks. He says treatment horses’ clinical signs (e.g., coughing), lung function, and BALF results improved as compared to the placebo group, and owners detected signs of improvement within one week. The team concluded that feeding a product rich in this omega-3 fatty acid as part of a low-dust diet to horses with chronic airway disease for eight weeks was equivalent to administering a three-week course of the anti-inflammatory medication dexamethasone with a diet not considered low-dust.
Barn Cleanliness and Bedding
While it’s important to keep stables relatively clean and free of airborne particulates and ammonia, keep in mind that even the cleaning process can be harmful to your asthmatic horse. Van Erck-Westergren suggests that barn owners strip all stalls completely and clean/disinfect surfaces thoroughly once per month while horses are turned out. Afterward, allow the barn to air out until dry before bringing the horses back in, so they’re not exposed to the dust and/or chemicals. Also keep your barn clutter-free so items lying around don’t accumulate dust that you’ll inevitably stir up when you use or move them.
Couëtil suggests waiting at least an hour after stall-cleaning to bring horses in. And all three of our sources recommend using low-dust bedding options, such as shavings, peat, and shredded paper or cardboard, rather than straw, which can be very dusty.
“The quality of straw depends on climate and harvest and is very difficult to control and assess before purchase or opening of a bale,” says van Erck-Westergren, adding that straw alternatives such as pelleted bedding and flax can be surprisingly dusty, as well.
Mazan says horses don’t even need bedding if they have stalls with mats and access to a comfortable area in which to lie down outside.
Victories with Ventilation
Air circulation is very important for stabled horses, especially those with equine asthma. “We are comfortable at temperatures around 25° Celsius (77° Fahrenheit), but horses are comfortable at a temperature of around 10°C (50°F), so leave the windows and doors open as much as you can in winter and fall,” says van Erck-Westergren. “You can cover up.”
Van Erck-Westergren recommends keeping asthmatic horses that must be stabled in well-ventilated stalls with open windows or doors (i.e., with stall guards or openings above the stall door where the horse can hang its head outside or in the aisle) and openings at the roof. Such barns offer good air renewal. Store hay and straw as far away from affected horses as possible—preferably in a different building.
“If you have cobwebs, traces of moisture, or mold patches on the ceiling or walls, if there is a strong smell in the stables in the morning, and if the atmosphere feels stuffy, you know the ventilation is insufficient,” van Erck-Westergren says. Dusty arenas, round pens, and paddocks can also be sources of exposure, especially if horses move between stalls and arena often.
While managing your horse’s environment is paramount, sometimes your veterinarian must use medical approaches to reduce inflammation and improve breathing.
“For this, corticosteroids are the only efficient anti-inflammatory drugs to control RAO and IAD,” says van Erck-Westergren. Because these drugs have secondary effects, “administration by aerosol therapy (nebulization) is recommended once the horse’s breathing is stabilized. In horses that have labored breathing and bronchospasm (a temporary constriction of the airways into the lungs caused by muscle contraction), rapid relief can be brought by (these) bronchodilators. Mucolytics (which dissolve mucus) can also be useful, as chronically affected horses will produce a thicker, more abundant mucus that can clog the smaller airways and maintain coughing.”
Because RAO and IAD are not infectious, she recommends against administering antimicrobials, “unless a complicating pathogen has been isolated in the respiratory samples and tested for antimicrobial resistance.”
In the long term, the best course of action when managing any horse is to reduce his exposure to environmental allergens and dust as best you can. And if your horse does suffer from equine asthma, heed your veterinarian’s advice, follow our sources’ tips, and be constantly thinking about how to improve your barn and property’s air quality. Luckily, proper management can greatly improve the outcome for many equine asthma cases.