How air pollution affects your horse’s health

Our warming climate poses health risks for horses and people alike. Here's what you can do to protect your horse against the worst effects.

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It was another brutally hot day in Maryland. Haze from the California wildfires stretched clear across the country that week, coloring the setting sun dark red. I stood with my horse Luciano in the growing dusk, hosing him off for the fourth time that day. His nostrils worked faster than I wanted to count, but I estimated that his respiration was upward of 50 breaths per minute. His skin was hot to the touch, but he only sweated in small patches behind his ears and around his nostrils.

Horse in paddock during California wildfires. (Adobe Stock)

I pictured the struggle that went on in his body each day. Foremost was PPID (pituitary pars intermedia dysfunction), a metabolic condition affecting the hypothalamus and pituitary glands that causes a whole host of problems, from abnormal hair growth to insulin resistance. Anhidrosis (no or abnormal sweating) can be a component of PPID. In Luciano’s case the condition was severe enough to need targeted treatment.

Equine asthma, inflammation of his lower airways, was the latest in his string of diagnoses. The conditions were unlucky coincidences that worked together to make him miserable. Every day warmer than 80 °F, he panted even just standing in his pasture, unable to sweat and struggling to draw air into his inflamed lungs. My sister and I had retired him from our college riding program when he was 20 years old. And he now received all the medication he needed. But we were fighting years of health challenges and stress on his lungs.

Luciano’s breathing slowed as the cold water from the hose worked its magic. His eyes (round with a perpetually sweet expression, like a Jersey cow) brightened and he nudged my arm in search of treats. I slipped him a piece of carrot from my pocket and switched off the hose.

“It’ll be another hot day tomorrow, buddy. Try not to need this again before noon, okay?”

More hot days

Over the last 50 years, the number of above 90-degree days in Maryland has increased from 20 days annually in the 1960s to 49 days in 2019. Climate change not only influences the frequency of extreme heat events, but also affects our air quality. Air pollution can make breathing difficult for people (and horses) with respiratory disorders. Watching Luciano struggle, I was certain that the combination of heat and poor air quality were making it difficult for him to breathe as well.

Upon speaking with two veterinarians from the Colorado State University (CSU) College of Veterinary Medicine and Biomedical Sciences, I found he was far from the only horse whose health was affected by climate change.

“People are seeing the effects of [climate change on their horses], but I don’t think they’re realizing the whole picture,” says Katie Seabaugh, DVM, DACVS, DACVSMR. Climate change has numerous effects on equine health. Altered weather patterns cause heat stress and longer warm seasons prolong the life cycles of pathogens and internal parasites. Climate change leads to more frequent and severe disasters that can affect horses directly or necessitate their transport to safer areas. For many horse owners in the eastern United States, the most observable effects are those brought on by extreme heat and air pollution.

Approximately one in 10 mature horses have some level of lower airway inflammation. Typically, this inflammation (which results in conditions previously known as inflammatory airway disease/IAD and recurrent airway obstruction/RAO, but now referred to collectively as equine asthma) is commonly caused by environmental irritants such as dust and pollen. Research shows that equine asthma can also be caused or exacerbated by airborne particulate matter from wildfire smoke as well as air pollution from other sources.

Perils of particulate matter

Air pollution has other body-wide effects. Colleen Duncan, DVM, PhD, DACVP, DACVPM, a colleague of Seabaugh’s, told me about a study by their CSU team that measured the effects of air pollution in dairy cattle. Researchers found an association between airborne fine particulate matter, known as PM 2.5 (particles that are 2.5 micrometers or smaller in diameter), and the volume and composition of milk produced.

Particulate matter (PM) varies in size depending on its source. Some particles,
such as dust, soot or smoke, can be seen with the naked eye. Mold, pollen and
other types of very small PM can only be detected with an electron microscope. 

When PM 2.5 was elevated, cows produced less milk and had higher somatic cell counts (SCC) in the milk. SCC are typically elevated in response to the disease mastitis in which the teats become infected. But cows in the study did not have mastitis and the research team hypothesized that the elevated SCCs were due to an increase in systemic inflammation secondary to the pollution exposure.

PM 2.5 particulate matter is small enough to enter the bloodstream, where it can travel beyond the lungs to other parts of the body. In people PM 2.5 exposure is a major risk factor for heart disease. For this reason, Duncan and Seabaugh have been investigating the impact of air pollution on equine athletic performance. The Environmental Protection Agency’s national ambient air quality primary (health-based) standard for PM 2.5 is currently 12 μg/m3.

However, new human health and science information has prompted a policy review and a proposal to update the standard to the range of 9.0 to 10.0 µg/m3. The CSU research team has similarly found that PM 2.5 levels as low as 7 µg/m3 can negatively impact the speed of Thoroughbred racehorses with thresholds of around 10 and 11 µg/m3 having the greatest impact. Collectively this work suggests there may be several, yet unmeasured, effects of pollution on horses and other animals.

A bodywide effect

Duncan says air quality can vary greatly depending on pollutant concentration and local weather conditions, but she thinks there is likely an association between air pollution and several disease conditions, including equine asthma. Little research has been done in this area yet, but Duncan suspects that “we will find increased numbers of horses diagnosed with this problem, especially in certain [parts of the country]. But, to my knowledge, that [research] just hasn’t been done yet.”

Air quality is just one factor in equine respiratory health, Seabaugh adds. Horses “have an incredible lung capacity, far more than any of our other [land] species … and they [also] use their lungs as a cooling mechanism.” Equine lungs are massive (the third-largest organ in a horse’s body) and exchange about 60 liters of air per minute at rest, or the equivalent of four water buckets.

The lungs also contribute to thermoregulation by warming and moistening air as it enters the body and dissipating excess heat through air exchange. The warmer the ambient air is, the more difficult it is for the horse to cool down. External air is typically cooler than the horse’s body temperature, which aids in cooling. But with global temperatures rising, the outside air sometimes isn’t much cooler than the horse’s body.

Counties with the worst air pollution
Mapping average fine particulate-matter-pollution, 2000-2016. Fine particulate-matter pollution consists of microscopic particles that come from burning fossil fuels. It can cause respiratory conditions in people who live in heavily polluted areas. 

The Earth’s temperature has risen by about 0.14° F per decade since 1880. In the past 40 years that figure has climbed to 0.32° F per decade. In total, that is an average temperature increase of two degrees Fahrenheit. People are starting to feel the impact of rising temperatures, and so are their horses.

When Seabaugh was a practicing veterinarian in Georgia, she “often found horses that had airway problems [and] really struggled in the heat, and would frequently … shut down their ability to sweat. “It became this trifecta: couldn’t breathe, couldn’t cool down, couldn’t sweat.”

Looking to the future

I pictured my own Luciano as he had been all summer of 2021: bay coat clipped so short that his soft hair was more mousy gray than rich brown, flanks heaving even in the shade as he struggled to draw air into his inflamed lungs. His coat was always bone dry, with maybe some sweat around his fuzzy ears (he hated the clippers near them so that hair always stayed long) or rolling in beads down his nose. A normal equine respiration at rest is 12 to 16 breaths per minute. But Luciano was typically upwards of 50 breaths per minute just standing in the pasture.

His veterinarian diagnosed Luciano’s respiratory problems in September 2021, and we started treating him with a nebulizer, which made a huge difference in his lung function. But I did not get to finally see him thrive the next summer as I had hoped. He came down with a severe case of colic in December 2021 and my sister and I made the devastating decision to euthanize him. I am so glad that we were able to take him in and make his golden years happy. But I am angry that he went so long without the medication he needed.

Unfortunately, as Seabaugh and Duncan have shared, Luciano is far from the only horse to struggle with these conditions. Climate change will continue to affect weather patterns and air quality—so how can horse owners protect their animals’ health?


“You can vote!” Duncan exclaims. “It matters in your local elections if they put three extra lanes on the interstate beside where you board your horse. It also matters what we do at the national and international level. In the last weeks, much of the United States has experienced terrible air pollution coming from the fires in Canada. Climate change is a global issue, and we must work together to protect the health of animals and people alike.”

Make smart choices

On an individual level, there are risk factors that you can control and, she concedes, those that you can’t. You can’t remove pollutants from the air but you may be able to avoid adding more to your horse’s environment during periods of poor air quality. Things like watering the barn aisle before sweeping, soaking your horse’s hay and choosing low dust bedding will all help. You can ease the impact of heat on your horse by riding in the coolest part of the day, ensuring that your horse has access to shade and providing abundant fresh water in turnout.

Share your views

Of course, sometimes someone else is setting the schedule. Competition, clinic and lesson organizers will increasingly need to take equine heat stress into account when planning events. So far, “there has been a lack of attention to this in the equine sport industry,” says Duncan. “Horse show schedulers are probably going to be the last ones that we get on board,” because they are trying to make a profit. Seabaugh agrees, but adds that advocating from an equine health perspective could make a difference.

Although some people still may argue about climate change, “everyone agrees about health,” Duncan says. “We don’t need to wait for more information to act.”

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