The barn environment is replete with organic particulate matter, respirable endotoxin, molds, and volatile gases such as ammonia. The worst offenders appear to be hay and straw. Multiple studies have shown that significant improvements can be made by replacing dusty substrates and feed with less dusty substitutes. (Kirschvink 2002 For instance, pelleted hay and wood shavings are often better than regular hay and straw bedding, but outdoor living, in most cases, is the best. What is not clear to many owners is that even small or transient contacts with hay can initiate severe signs, and should be avoided. (Fairbairn 1993)Indoor arenas present another high dust challenge to the horse, with respirable particulate levels 20 times that which has been recognized to cause respiratory dysfunction in humans. (Millerick-May VCRS) In addition to changing to low dust feeds and beddings, the following recommendations to owners should be made:
- Feed hay from the ground, not from a hay net
- Soak hay well before feeding or use ensiled or baked hay products
- Wet any dusty grain (e.g. pellets) before feeding
- Sprinkle aisle ways with water before sweeping
- Avoid storing hay overhead. If unavoidable, lay a tarp under the hay to avoid dust raining down on the horses
- Use a humectant or hygroscopic agent to reduce dust in the indoor and outdoor arenas
- Remove horses from the barn while cleaning stalls or moving hay
- Do not use blowers to clean aisles
- Remove cobwebs and other dust collectors routinely when horses are out of the barn
An over-arching principle that can be derived from the OSHA Dust Control Handbook is that prevention is better than cure. In addition to the well-known presentation of summer pasture-associated recurrent airway obstruction in hot, humid southern states, it is important to remember that horses in New England can also have disease that presents primarily in the spring and summer, and that seems to improve when horses are kept temporarily in clean, non-dusty indoor environments.
It is of critical importance to take an in-depth history to try to document environmental triggers. For instance particulates associated with feeding from a haynet versus feeding from the ground is one of the most important risk factors for the development of airway inflammation, so identifying a simple-to-fix risk factor could be of considerable help. A very thorough inspection and assessment of the horse’s environment will be important for remediation. For instance, if the history suggests that the horse is consistently worse in the spring, whereas clinical signs are abated in the barn in the winter, it suggests that the worst culprits for this horse are the molds and pollens associated with moist warm weather, and the clinician may prescribe clean indoor living for the horse during that period. It is very useful for the owner or trainer to keep a diary for the affected horse, noting when exacerbations occur. Simple interventions, such as opening the barn doors or making sure to feed hay off the ground can significantly decrease the number of particulates that a horse breathes. Endotoxin levels are lower at the breathing zone in horses at pasture than in stables, which may explain why outdoor living benefits many horses with lower airway inflammation.
A recent review of environmental factors in equine asthma shows that using haylage v. hay results in a 60-70% decrease in exposure to particulates, and that even soaking hay results in a 50% decrease in exposure to particulates. Other things that help significantly are feeding a pelleted feed, and late harvest or second cutting hay. (Ivester, Couetil, Zimmerman, JVIM 2014, 28) Similarly, non-dusty shavings for bedding are better than straw, and paper or pelleted bedding is better than shavings. Good ventilation in the barn is also important, and a trained barn architect can be very useful in this regard. Recently it has been shown that omega-3 fatty acids confer added protection to a low-dust environment. (Couetil 2016)