Smoke Inhalation in Horses

Smoke from bushfires and wildfires can cause serious health problems for all animals, including horses. Smoke contains toxic chemicals, such as carbon monoxide, sulfur dioxide, hydrogen cyanide, hydrogen sulfide, and ammonia. These substances, in addition to particulate matter and superheated gases, can lead to thermal and chemical irritation of the eyes and respiratory tract.

The horse has enormous lung capacity and moves great volumes of air into and out of its lungs. Large airborne particles (>5 microns) are filtered out in the upper respiratory tract, while smaller ones may be expelled when the horse exhales. Smoke contains minute particles (<1 micron) that migrate deep into the lungs and settle there, causing damage to tissues and adversely affecting health and performance. Damage from smoke also compromises normal defense mechanisms of the lung and makes the horse more sensitive to the inflammatory effects of bacteria and pollen. Further, smoke aggravates symptoms in horses with pre-existing asthma.

Tissue damage from smoke exposure often causes coughing, lethargy, elevated heart rate, nasal discharge, and fast, shallow breathing. Fluid may accumulate in the lungs, and the horse may develop a fever. Pneumonia sometimes develops following smoke inhalation, and chronic exposure usually leads to mild equine asthma.

The respiratory rate of a calm horse at rest should be 12-24 breaths per minute (bpm). Horses should be examined by a vet if any of these signs are observed:

• Resting respiratory rate more than 30 bpm,
• Obvious flaring of nostrils,
• Wheezing or noisy breathing,
• Increased effort of breathing with the development of a “heave line” along the horse’s lower abdomen,
• Repetitive or deep coughing, or
• Abnormal nasal discharge.

Treatment of acute smoke inhalation varies by horse, but recommendations include high doses of the antioxidant vitamin E. Natural sources of vitamin E, as found in Nano-E, are recommended. Nano-E has higher bioavailability than other vitamin E supplements and can increase blood and tissue levels quickly.

After acute smoke inhalation, the horse may need 4-6 weeks off to recover before returning to training, even if it does not require veterinary intervention. A minimum rest period would be 2 weeks. The well-documented pulmonary anti-inflammatory effects of long-chain omega-3 fatty acids in supplements such as EO-3 can be used to speed recovery of lung function and health.

What about chronic exposure to smoke when it is moved by wind long distances from the fire zone? The smoke can remain for days or weeks, such as in Calgary in 2018, when a large area was blanketed in smoke for 6 weeks.

Air quality diminishes when smoke is visible, so horses should not be exercised if smoke is present. If the smoke irritates your eyes, you can assume it is bothering your horse’s eyes and lungs, too. While humans can wear masks and move into smoke-free environments, horses cannot. Limit exposure to smoke when possible, and avoid anything more than light exercise in smoky conditions. Veterinary treatments, including bronchodilators, corticosteroids given by nebulizer, and long-chain omega-3 fatty acids, can be used to reduce the impact of chronic exposure to smoke on lung function.

During the Calgary fires, researchers at the University of Guelph studied the effect of smoke on lung function and performance in a group of fit polo ponies. All horses were coughing at rest and during work, and riders observed reduced performance. Lung washes were performed, and all horses showed signs of mild equine asthma, including inflammation.

With smoke in the air, a maximal exercise test was conducted that recorded speed and VO₂max, a measure of oxygen uptake from the lungs. Later on, after nearly three weeks of smoke-free air, horses had a 15% increase in speed, with a similar increase in VO₂max. This study demonstrates the profound effect of smoke on a horse’s lung function and performance.

Air quality index (AQI) gauges the safety of certain exercise for human athletes, and this number can be used to assess the safety of equine exercise in smoky environments. This index has been used as the basis for cancelling race meetings and equestrian events hundreds of miles from the bushfire zone in Australia in the summer of 2019/2020. Moderate to intense exercise should be reduced or limited in sensitive horses when AQI is over 100. AQI over 200 is considered extremely unhealthy, and training or competition should be postponed or cancelled. Event organisers should consider AQI and its effect on equestrian health and welfare when conducting events in smoke-filled air.

Bond, S., P. Greco-Otto, J. MacLeod, A. Galezowski, W. Bayly, and R. Leguillette. 2020. Efficacy of dexamethasone, salbutamol and reduced respirable particulate concentration on aerobic capacity in horses with smoke-induced mild asthma. Journal of Veterinary Internal Medicine. doi.org/10.1111/jvim.15696

 Couetil, L.L., J.M. Cardwell, V. Gerber, J.P. Lavoie, R. Leguillette, and E.A. Richard. 2016. Inflammatory airway disease in horses: Revised consensus statement. Journal of Veterinary Internal Medicine 30:503-515.

 Magdesian, G. 2017. Treatment of smoke inhalation in horses. UC Davis VMTH Large Animal Clinic.

 Nogradi N, L.L. Couetil, J. Messick, et al. 2015. Omega-3 fatty acid supplementation provides an additional benefit to a low-dust diet in the management of horses with chronic lower airway inflammatory disease. Journal of Veterinary Internal Medicine 29:299-306.