How Wildfire Air Is Rewriting the Summer Show Calendar

The sky over much of the Midwest has been the wrong color for three days. Not storm-grey — a flat, filtered orange that makes arena lights click on at two in the afternoon. It is not weather in the usual sense. It is smoke, and it has already closed the show ring.

A Week of Cancellations

Smoke from more than 836 active Canadian wildfires has pushed unhealthy air deep into the US Midwest and Northeast, and the disruption has not stayed confined to travel. The Traverse City Equestrian Festival in northern Michigan canceled all events as ash fell and organizers watched air quality plummet. In Ontario, Environment Canada issued an orange-level air quality warning for Guelph and Wellington County, recommending that outdoor sports events be canceled or rescheduled, and Grand River Raceway pulled its card accordingly.

The scale of the source event is worth sitting with. Nearly 3,500 fires have burned more than 4.8 million acres across Canada this summer, with new blazes flaring in Ontario in recent weeks, while stateside fires have separately burned more than 3.6 million acres, mostly across the western half of the country. Minnesota's West Duluth air quality monitor logged a new state record for wildfire smoke concentration this week, and dense smoke has settled over Green Bay, Detroit, Cleveland, Columbus, and Rochester. An estimated 100 million Americans have been exposed to potentially unhealthy air as a result.

For a barn, that translates into a judgment call organizers have had to make on short notice, with little precedent to lean on.

What Smoke Actually Does to a Horse's Lungs

The instinct is to assume a horse simply tolerates smoke better than a person does — bigger animal, bigger lungs. The research says close to the opposite. Athletes are especially vulnerable to air pollution because their total airway exposure is magnified by the volume and rate of air they move during exertion, and a horse at speed moves considerably more air per minute than almost any human athlete.

A 2025 Equine Veterinary Journal study out of Colorado State University's College of Veterinary Medicine and Biomedical Sciences, led by researcher Linda Kim, pulled together the existing evidence on ambient air pollution and Thoroughbred performance. Among the findings: horses in Ontario exposed to elevated weekly mean PM2.5 and nitrogen dioxide showed a greater risk of lower airway inflammation, and racing Thoroughbreds exposed to fine respirable dust showed a statistical association with equine asthma, with measurable drops in speed figures tied to the proportion of inflammatory cells present in airway samples. In a separate finding involving polo horses naturally exposed to wildfire smoke, it was improved environmental conditions — not treatment — that reduced clinical signs and restored athletic performance.

The underlying research trail on this runs through Ontario as well. Work out of the Ontario Veterinary College, led by researcher Janet Beeler-Marfisi, established that increased weekly mean PM2.5 and nitrogen dioxide levels were associated with a higher proportion of inflammatory cells in the lower airways of horses — one of the first studies to draw a direct line between ambient pollution and equine lung inflammation rather than just human asthma data. On the European side, the Royal Veterinary College in London has been part of the international group behind the modern equine asthma classification — a 2019 Havemeyer Workshop that brought together researchers across multiple countries to unify how airway inflammation in horses is diagnosed and discussed, work that now underpins much of how vets talk about exactly this kind of exposure.

The Governance Gap

Here is the part worth sitting with longer than the smoke itself: there is currently no equine-specific guideline for when air quality crosses from tolerable to dangerous for a horse. Show organizers this week made the call to cancel using human air quality indices, general caution, or simply the color of the sky — not because that is wrong, but because nothing more specific exists yet. A horse's respiratory demands are not a human's, and the research to build a horse-specific threshold is still catching up to how often this is now happening.

That gap sits at the center of a broader pattern in equestrian governance: welfare-adjacent decisions increasingly get made in the absence of formal standards, by whoever is closest to the horse that day. It has worked, mostly, because barn managers and organizers tend to err conservative. But conservative judgment calls made without shared benchmarks produce inconsistency — one show cancels at an AQI that another runs through, and a horse that ships between the two carries the same lungs to both.

None of this requires panic. It requires the same instinct that already governs footing and heat: checking before you ask for effort, and accepting that the ring can wait a day.