October 2020 - After The Smoke Clears?
Written by CRM
Thursday, 01 October 2020 16:10
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fires

Better safe than sorry when it comes to timing of exercise after smoke exposure.

The wildfires’ effect on horses will linger long after the smoke clears. That was the main takeaway from a September 16 livestream Zoom call with Dr. Phoebe Smith of Riviera Equine Internal Medicine and Consulting and Drs. Mark Revenaugh and Austin Rowland of Northwest Equine Performance.

Revenaugh and Rowland spoke from their practice in the Portland, OR area, where the Air Quality Index was in the “deep purple” zone of 400s, noted Dr. Revenaugh. (That’s actually maroon and on the most severe end of Airnow.com’s AQI chart).

 


Very prominent in all other aspects of equine care, the Portland vets didn’t have deep experience treating horses dealing with smoke inhalation. So, they turned to Dr. Smith to ask their own questions and address the most common inquiries of their horse owning clients.

 

In addition to being an internal medicine specialist, Dr. Smith has a mobile practice based in Central California. That has put her many times on the front lines of helping owners care for their horses through the aftereffects of California’s too frequent fires.

The following is a paraphrased recounting of this extremely helpful and important conversation. It can be found it its entirety on Northwest Equine Performance’s Facebook page.

Dr. Revenaugh: Where we are the AQI is 440. What does that mean?
Dr. Smith: The Air Quality Index is a measure of air quality that spans from 0 to 500. The numbers are derived from multiple factors that affect air quality. With the current wildfires, the most significant of these is particulate matter in the air. Up to 100, the air quality is acceptable, with the possible exception of for those who are unusually sensitive to air pollution. Over 300, everyone is likely to be affected and there’s a hazardous health warning for all.
Particulate matter is what we’re dealing with now. Particles above 5 microns in size can usually be filtered out of by natural defense mechanisms in the horse’s upper airway. Smaller than that, they get stuck way down deep in human and horse’s lungs.  What we’re seeing is the number “pm2.5,” meaning very tiny particles of everything that’s burning now: wood, plastics -- everything in the homes and cars, etc.
Dr. Revenaugh: The crux of this conversation is that, in addition to getting oxygen into the blood stream, the lungs function as an air filter. If you look at an air filter in your house, you know that the more air passes through it, the dirtier it gets. The horse being a living species, however, you can’t just replace the filter. It is a long process to get those particulates out of the respiratory tract.
Dr. Rowland: There are no large volume studies in equines about the impact of smoke and particulate inhalation, so we extrapolate information from studies with human athletes. What do we know from those?
Dr. Smith: We use similar AQI guidelines and recommendations as far as when it is safe to be outside, to exercise and to return to work after the smoke has cleared. Above 150, everybody is affected to some extent. Above 200, it’s not safe for anyone to exercise -- horse or human.
In humans, there is information documenting hospital admission rates during times of smokey air. In addition to respiratory distress, they’ve also found problems with blood pressure and cardiac disease. We don’t know about cardiac issues in horses related to smoke inhalation.

Dr. Rowland: What is the consensus regarding the risk of exercise to a horse when the smoke has cleared and the air quality becomes acceptable?  
Dr. Smith: That is probably the hardest question: When can you start riding? The answer is a minimum of two weeks after the smoke has cleared, and it can be up to six weeks depending on the amount of smoke in your area. Thinking of the lung as an air filter, the lungs just can’t be cleaned that quickly.
We’re talking about “respiratory rest,” the state in which the horse is not breathing hard, or fast, or deeply. The idea is to minimize the volume of air moving through the lungs.

Dr. Rowland: What are the ramifications of putting a horse back to work too soon?
Dr. Smith: At a minimum, decreased performance. It may be that your horse is not acting badly, but he is not getting maximal performance because the oxygen levels he’s getting are reduced up to 20 days after smoke exposure. So, best case, he won’t have the same level of performance, and not just in terms of speed or respiratory recovery rate. Oxygen is needed for the function of muscle, brain, tendon, limbs, etc., so it’s a decrease in performance of all the body’s systems.
The worst case scenario is that particulate matter causes inflammation that persists after the air clears. That results in broncho constriction -- a narrowing of the airways. If you work a horse with inflamed lungs hard, residual inflammation from smoke exposure could become worse than it was before the exercise.
    
Dr. Revenaugh: With horse shows coming back, everyone wants to show. How quickly can people get back to that? What are the guidelines to know if it’s a good idea to compete or to ship the horse off to a competition?
Dr. Smith: I keep hearing “Well the air quality is good where the show is.” But if your horse has been living with smoke inhalation, then he needs a minimum of two weeks after the air has cleared. That’s both for his airways and his muscles and tendons, etc. Besides considering the lungs, if you haven’t been able to ride for three weeks, are your horses’ legs ready to exercise?

Dr. Revenaugh: What about turning horses out?
Dr. Smith: That depends on local air quality, the air quality inside the barn and whether or not the horse will be wild and wooly running all around. If he’s going to walk around a little in a 12 x 12 paddock, that’s OK if the air quality is OK.
If possible, you could sprinkle the pasture to reduce the particulate matter in the air.
    
Dr. Revenaugh: If the horse is worked too hard too soon, could the end result be compared to horse with asthma or heaves? Because what we’re talking about in these conditions is particulate matter and the body’s reaction to particulate matter.
Dr. Smith: Absolutely! In fact, asthma is a sequelae (consequence) of smoke exposure. The asthma can be mild, but it could be severe asthma depending on the severity of exposure, and sensitivity of the horse’s airways. That’s what we don’t know exactly. It means that training should be put on hold so that mild asthma created by smoke inhalation is not exacerbated and put over the edge by exercise.

Dr. Revenaugh: How can we mitigate the damage from smoke inhalation?
Dr. Smith: The most basic is to try to minimize exposure. Then, ensure respiratory rest for the horse. Keep the airway moist. Provide water, keeping in mind that horses usually consume the most water within two hours of eating. You may want to wet the hay.
Dry airways are sticky; particulates tend to stay there. A moist airway is more able to remove particulates through normal defenses.

Dr. Revenaugh: What symptoms give a clue that the horse is struggling when he’s returning to work?
Dr. Smith: The obvious sign is that, if your horse was doing fine with hand walking, then started coughing at the trot. The more subtle signs are nostril flair and a higher than normal respiratory rate. Normal is 12-24 breaths per minute, and a rate above 30 can be a symptom of trouble. Also, your horse might just seem a little off.
These are among many areas where it’s so important to know what’s normal for your horse. If any of these symptoms occur, call your horse’s veterinarian. He/she is the one who can determine if the issues are coming from smoke-related respiratory inflammation or from a secondary bacterial infection.  

Editor’s Note: This wonderful discussion also touched on the pros and cons of various medications, supplements and treatments for protecting equine respiratory health during smoke exposure. Every answer began with consulting your horse’s veterinarian because of the multiple variables involved. As of Sept. 22, this discussion was posted on Northwest Equine Performance’s Facebook page and we highly recommend it. Thanks to these veterinarians for generously sharing their time and knowledge so widely.