In well-trained horses, the respiratory system is one of the main limiting factors on performance. In the Northern Hemisphere, 10-20% of adult horses suffer from severe asthma, while more than 80% have mild asthma.
Asthma produces variable signs. While horses show no obvious signs of a problem at rest, a mild form impacts performance and recovery, and affected horses often have an intermittent cough and nasal discharge. Horses with moderate to severe asthma frequently experience cough and nasal discharge. They also demonstrate an increased respiratory rate and effort visible as nasal flare and pronounced expiratory abdominal lifts. Exercise intolerance is another common outcome of severe asthma – even small increments in lower airway inflammation have significant impacts on performance.
Katie Sheats, DVM, PhD, Dipl. ACVIM, assistant professor of equine primary care at North Carolina State University, in Raleigh, describes various mitigation strategies to prevent equine asthma when she spoke at the 2022 American Association of Equine Practitioners (AAEP) Convention held Nov. 18-22 in San Antonio, Texas.
To optimize equine respiratory health and detect issues early, Sheats emphasized the importance of horse owner recognition of clinical signs. She also recommended horse owners know the potential triggers that cause irritation to the respiratory tract in the barn, arena, and pasture, as well as from feed materials. One notable trigger is endotoxin, which is found in manure. Other triggers include fungi and molds found in feed and bedding. Noxious gases from urinary ammonia fumes and tractor exhaust within a barn or arena can also pollute the airspace. Particulate matter and dust circulate within the barn when horses are fed and eating hay, are stamping and moving around in bedding, and during stall cleaning. Heat and humidity are contributors, as well, making hot days tough on respiratory performance, she said. Cases of severe equine pasture asthma (EPA) are exacerbated in horses on pasture from summer to fall. Sheats said this syndrome tends to occur with high temperatures and humidity and is especially prevalent in the southeastern U.S.
Different sizes of inhalable particles attach at different levels of the airway. The most concerning ones are particulate matter (PM) 5 and 2.5, which are the respirable dust and fine particles that settle in the lower airways. PM-10 type dust, such as pollen, isn’t likely to reach deep into the lungs.
Sheats said managing feed particles has the greatest impact on respiratory health. She recommends:
- Avoiding hay-nets, which increase respirable dust fourfold compared to ground feeding.
- Avoiding round bales.
- Soaking hay for 30-60 minutes and feeding it wet.
- Steaming hay to decrease mold, endotoxin, and respirable dust, though this strategy might not entirely control a horse with already established equine asthma.
- Feeding pelleted products or haylage to significantly decrease airway inflammation.
Another helpful strategy is decreasing dust exposure during barn cleaning and maintenance, in high-traffic areas and arenas, and when feeding hay. Store hay in a different area outside the barn rather than in a loft overhead. Don’t use straw bedding; instead use peat, shredded paper, or cardboard bedding, or mats with no bedding. Wet down arena surfaces to diminish dust.
Barn cleanliness is important, but horses should be moved outside during use of rakes, leaf blowers, and diesel tractors. Sheats recommended allowing dust to settle for 30-60 minutes before bringing horses back inside. Increase barn ventilation by keeping doors and windows open. Turn horses out on pasture to significantly decrease exposure to endotoxin unless they’re at risk of equine pasture asthma. Lastly, remember that environmental airway irritants affect not just horses but also people.