Most approaches to solving "roaring" in horses--a noisy, performance-limiting condition of the equine airway--involve wielding a scalpel, but a Cornell University-based research team recently examined an alternative, treatment for roarers. Jon Cheetham, VetMB, PhD, Dipl. ACVS, of the College of Veterinary Medicine's Department of Clinical Sciences described this approach at the 2011 American Association of Equine Practitioners convention, held Nov. 18-22 in San Antonio, Texas.
"Recurrent laryngeal neuropathy, also called roaring, is caused by dysfunction of the left recurrent laryngeal nerve resulting in paralysis, either partial or complete, of the left arytenoid cartilage," Cheetham explained. "This paralysis of the arytenoid cartilage, which is part of the larynx, causes poor performance because the airway collapses during exercise, preventing enough air from reaching the lungs. With too little air, the horse's muscles can't generate enough energy to contract and function properly."
Roaring is a fairly common problem, affecting an estimated 8% of all Thoroughbreds, as well as many sports horse and draft breeds. As Cheetham previously told TheHorse.com, the current treatment of choice is a "tie-back" surgery to permanently open the abnormal arytenoid cartilage. The overall success rate is moderate (48-68%)..
As an alternative to surgery, Cheetham and colleagues assessed the feasibility of "functional electrical stimulation," or FES, in horses diagnosed as roarers.
"FES is a way to both train a particular muscle and cause it to contract during exercise using very small pulses of electrical current," Cheetham said.
The goal of FES is to stimulate the target muscle, which in the case of roaring is the dorsal cricoarytenoid (DCA) muscle, and essentially force it to contract. Contraction of this muscle causes the arytenoid cartilage to be pulled back to the "open" position to let air pass, as would normally occur in an exercising horse.
To test the procedure Cheetham et al. fitted six horses with intramuscular FES units in the DCA muscle. They determined that stimulation of the DCA muscle resulted in a significant improvement in arytenoid abduction at all levels of exercise intensity.
Cheetham said that FES therapy is indicated for Grade 3 roarers (which represents asynchronous movement, but the arytenoid cartilage cannot open fully during maximal exercise). He also noted that while research is still needed on the treatment modality, scientists have learned much since the project began.
"FES is a promising strategy for restoring function in horses with denervated laryngeal muscles due to left recurrent nerve dysfunction," concluded Cheetham.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.