Reduce Recurrent Laryngeal Hemiplegia (aka Roaring) in Horses
‘Roaring’ is a degenerative upper-airway condition in horses. Find out what causes it, how it affects performance and how to treat it.
By: Nicole Kitchener |
A horse that makes a strange noise when he’s exercising at high speed could be a roarer with a lazy flapper. What’s that you say?
More technically, the horse might have recurrent laryngeal hemiplegia, a degenerative upper-airway condition generally referred to as ‘roaring.’ The condition occurs when the nerve supplying one or both of the cricoarytenoid dorsalis muscles near the larynx (the voicebox) is damaged and becomes fully or partially paralyzed.
What Causes Roaring in Horses?
The arytenoids, essentially big pieces of cartilage on either side of the larynx, usually close over the trachea (windpipe) when a horse swallows and then open quickly to allow breathing. When paralysis sets in, the arytenoid (colloquially “the flapper”) flops into the larynx. Because the larynx acts as a valve to regulate airflow into the trachea and then on to the lungs, the dangly bit not only creates the whistling or roaring noise, but due to reduced oxygen reaching the lungs, also results in progressive exercise intolerance.
“The horse won’t be able to meet their maximum performance. They’ll lose their air,” says Dr. Chris Bell, owner of Elders Equine Clinic, a Manitoba-based referral practice also serving southern Saskatchewan and Northern Ontario. A board-certified surgeon and adjunct professor at the University of Saskatchewan’s Western College of Veterinary Medicine, Bell and his associates predominantly treat sport horses. He says laryngeal hemiplegia is relatively common and they see it mainly in long-necked horses such as Thoroughbreds and draught breeds.
Although the exact cause of roaring is unknown, it’s usually attributed to direct trauma, incorrect injection of drugs (around the vein instead of inside) and as a secondary complication of disease or infection. It nearly always occurs on the left side, likely because the recurrent laryngeal nerve supplying the left side of the larynx is especially long, predisposing it to damage.
“It runs all the way down the neck, wraps around the base of the heart and then runs back up the neck,” explains Bell. “It’s an embryological thing. It’s how the body developed; a freak of anatomy.”
Diagnosis and Treatment of Roaring in Horses
Laryngeal hemiplegia first needs to be distinguished from other conditions that may cause respiratory noises such as infections, inflammation, lack of fitness or a displaced soft palate. It can be confirmed through an endoscopy exam involving insertion of a flexible video camera into the upper airway for observation. However, Bell says, the gold standard for diagnosis is overground endoscopy, where the veterinarian can see the larynx in “dynamic action.” The procedure involves fitting an endoscope and monitoring equipment to the horse so the veterinarian can watch the upper respiratory system during exercise in real time via Bluetooth technology.
Treatment usually consists of a surgical correction, most commonly a prosthetic laryngoplasty, often called a tie-back. During this procedure the cricoarytenoid dorsalis muscle is replaced with a suture to permanently open the arytenoid, Bell explains. In some cases, the horse may undergo a ventriculectomy either following laryngoplasty or rarely, on its own. This involves removal of a pocket of mucosal tissue (the ventricle) in the larynx to streamline the passage of air. Further, the vocal cords may also be removed. An arytenoidectomy, removal of all or part of the arytenoid cartilage, is sometimes done after a failed laryngoplasty or in the presence of abnormalities or infections of the arytenoid.
Bell also describes another surgery where the first or second cervical nerve is removed and implanted in the cricoarytenoid dorsalis. He says this “basically gives the muscle back its nerve supply from a different nerve.” A newer technique that also looks promising is semi-automated muscle replacements. A device is inserted that acts like a muscle to open and close the arytenoid.
A significant advancement in laryngeal hemiplegia treatment, Bell stresses, has been the ability to perform laryngoplasty with the animal in a standing position. “We don’t have to anesthetize the horse anymore. We just sedate them, extend their neck and we cut in [near the throatlatch] just like we would when they’re down. They’re fully awake during the procedure. When I’m doing it, I’m able to watch the arytenoid as I pull it back and put it in position.”
This method reduces many post-operative snags such as the arytenoid slipping back into the larynx. Standing laryngoplasty also eliminates the risk of general anesthesia, particularly in draughts and other large breeds which suffer an increased rate of complications due to their size. Persistent cough is the most common side-effect, usually as a result of aspiration of food by the permanently open larynx. Occasionally, pneumonia or infection occurs.
Non-surgical Options to Fix Roaring
Overall, the surgical success rate is quite high. However, roarers who aren’t required to reach maximum speed can experience continued success in competition without undergoing surgery. That is, unless the noise is considered an unsoundness, such as in the draught horse arena, or potentially rendering a horse unpinnable to hunter judges.
When surgery isn’t an option for practical, logistical or financial reasons, usually the best alternative is notching down the horse’s athletic career to a less strenuous level of competition, or even retiring him to become a pleasure mount. “They don’t require surgery to live,” notes Bell. “It really is a performance horse issue.”
Prevention isn’t possible other than avoiding administering your own intravenous injections and reducing the risk of trauma, says Bell. He recalls a situation that came through his clinic recently: “A group of chuckwagon horses had been getting ponied behind a truck. They only had ropes tied around their necks. All four of them came up as roarers.”