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Due to the high prevalence of equine asthma and its profound negative impact on quality of life, efforts directed towards managing flare-ups remain an important topic in equine medicine. Magnesium sulfate, a widely available and inexpensive medication used in human patients during asthma attacks, was recently evaluated in horses. Unfortunately, this product failed to yield positive results in a recent study.*

Currently, an estimated 15% of adult horses in the Northern Hemisphere suffer from severe equine asthma (recurrent airway obstruction [RAO] or heaves). When exposed to airborne allergens, such as dust and mold found in hay, these horses experience sudden constriction of the small airways, mucus accumulation in the airways, and remodeling of the airways, at times forever changing the anatomy and functionality of the respiratory tract.

“Treatment for horses suffering asthmatic flare-ups includes administration of injectable products that dilate the airways or inhaled products delivered by a mask placed over the horse’s muzzle,” explained Laura Petroski-Rose, B.V.M.S., a Kentucky Equine Research veterinarian.

A few problems associated with treating flare-ups include:

  • The expense associated with a veterinarian to administer injectable medications;

  • Common and notable side effects associated with those injectable medications, such as colic and increased heart rate, called tachycardia; and

  • Lack of availability or lack of tolerance of horses to inhaled products.

“Magnesium sulfate, based on its reported success in human asthmatics, induces relaxation of the airways during periods of severe asthma without colic and tachycardia,” shared Petroski-Rose.

Testing this approach for rescuing equine asthmatics during flare-ups, one veterinary team found that an intravenous infusion of magnesium sulfate improved clinical signs of asthma mildly but did not alter lung function. This result prompted the veterinarians to conclude that magnesium sulfate administration likely altered the horse’s breathing pattern only. They wrote, “Infusion of magnesium sulfate solution at the studied dose offers little advantage over currently used medications for the treatment of severe equine asthma.”

According to the veterinary researchers, owners should rely on tried-and-true approaches currently in place for managing equine asthma:

  • Antigen avoidance (limited stabling, clean hay, and other management strategies);

  • Routine use of anti-inflammatory corticosteroids to reduce inflammation in the airways;

  • Administration of bronchodilators to increase the diameter of the small airways; and

  • Use of omega-3 fatty acids (fish oil), such as EO-3 developed by Kentucky Equine Research, for additional anti-inflammatory benefits.

“EO-3 contains 9,450 mg of marine-derived fish oils, including EPA and DHA per serving. Top-dress this palatable product on your horse’s daily ration to support not only your horse’s respiratory health but also the reproductive, musculoskeletal, and cardiovascular systems,” Petroski-Rose advised.

*Tanquerel, L., G. Fillion-Bertrand, J.P. Lavoie, et al. 2018. Effects of magnesium sulfate infusion on clinical signs and lung function of horses with severe asthma. American Journal of Veterinary Research. 79(6):664-673.

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