Roaring in Horses – Left Laryngeal Hemiplegia

Updated December 15, 2023 | Reviewed By: Joan Maree Hinken, DVM, CVA, CVSMT

What is Roaring in Horses?

A dynamic endoscope image of the collapsed left arytenoid of a horse that roars.
A dynamic endoscope allows us to see the collapsed left arytenoid of a horse that roars.

Roaring is a term used when horses make a loud respiratory noise when exercised, immediately after exercise, when they’re breathing rapidly, or when the horse is startled (grunt test). The veterinary term for roaring is called Left Laryngeal Hemiplegia, meaning paralysis of half of the larynx. Horses that make this noise are also referred to as “roarers.”

Horses that suffer from this condition have a lack of nerve stimulation (innervation) to their left arytenoid cartilage which does not allow it to fully open. The severity of roaring can range from a slower abduction (opening) of the cartilage to complete paralysis of the cartilage.

Normally when a horse is breathing during exercise, his right and left arytenoid cartilages open outwards at the same time. They open the pathway of the larynx so he can breathe in maximum amounts of air. When there is an obstruction in the horse’s upper airway (in this case, sides of the larynx) it causes turbulence and hence a roaring noise.

What Does Roaring Sound Like in a Horse?

The roaring noise has been described as an unnatural sound, like a rattle, snore, or whistling during inhale, and even an unusual whinny. Roaring should not be confused with the vibratory noise made when horses flutter their nostrils as they sometimes let out a big breath or sigh.

What Causes a Horse to Roar?

A horse's larynx with grade 5 Left Laryngeal Hemiplegia.
Grade VI Left Laryngeal Hemiplegia.

In some cases, trauma has occurred to the left side of the horse’s neck in the jugular furrow or throat area. Roaring is caused when the left Recurrent Laryngeal Nerve, the nerve that stimulates the cricoarytenoid dorsalis muscle (which controls the movement of the left arytenoid cartilage) is damaged or inflamed. This either hinders or blocks nerve transmission, making the cricoarytenoid dorsalis muscle partially or fully paralyzed.

Many times, the exact cause of left laryngeal hemiplegia is unknown, so it is called Idiopathic Laryngeal Hemiplegia (ILH).

There are many theories about why some horses roar, but the exact cause has yet to be determined. One popular theory amongst veterinarians and researchers is that the left recurrent laryngeal nerve sustains damage as it is longer than the right recurrent nerve and has a different course through the horse’s body. Pathology studies of the horse’s nerve tend to support this theory.

Signs and Symptoms of Roaring in Horses

The usual sign of roaring is hearing the inhaling noise made by the horse when exercising, which is said to sound like a whistle to a loud snore. The noise increases in intensity the harder the horse breathes.

Onset usually occurs between two to seven years of age. Approximately 40% of Thoroughbreds and other large breeds of horses (notably Standardbreds) have varying degrees of abnormal abduction of the left arytenoid cartilage.

Depending on the intensity of work, the horse may show signs of exercise intolerance or a reduced ability to perform up to his normal abilities. The horse’s intolerance is dependent upon the degree of laryngeal collapse he has, his fitness, and the length and intensity of exercise.

Horses performing at lower levels of work, such as a beginner’s lesson horse, may not experience or show exercise intolerance. Roarers that are ridden in a manner that reduces or impedes their ability to breathe in enough air they need may exhibit more noise and a greater degree of exercise intolerance.

Diagnosing Laryngeal Hemiplegia

A horse wearing a dynamic endoscope.
A horse wearing a dynamic endoscope.

A thorough examination by a veterinarian may help to identify the cause of Left Laryngeal Hemiplegia especially if there is trauma or inflammation in the throat area. The larynx can be palpated to determine if there is atrophy of the cricoarytenoid dorsalis muscle.

A diagnosis of roaring is confirmed through endoscopy (or “scoping”). Since the arytenoid cartilages don’t abduct much when the horse is at rest, it is often necessary to perform the endoscopic exam immediately post-exercise or during exercise (called a dynamic endoscope).

There is a grading system used by vets to describe the degrees of abnormality in roarers. They range from I, which is synchronous full abduction of the cartilages, to IV, which is no significant abduction of the left arytenoid cartilage.

A horse being ridden while wearing a dynamic endoscope.

Treatment and Surgery for Roaring in Horses

The goal in treating roaring in horses is to restore the normal diameter of the rima glottidis or the opening between the vocal cords and arytenoid cartilages of the larynx. It also needs to prevent collapse of the vocal cord and arytenoid cartilage during inspiration.

The larynx has both digestive and respiratory system functions – making surgery a compromise. It must fully abduct (open) during strenuous exercise and fully adduct (close) during swallowing to prevent food or water from going down the wrong way.

A normal larynx of a horse viewed through endoscope examination.
A normal horse's larynx viewed through an endoscope.

Many horses can maintain their normal workload without surgery. There are many hunters and jumpers who have this condition and continue to compete successfully. Horses that are used for pleasure, trail riding, and light work can also live useful lives without undergoing surgery. Remember that if a roarer is experiencing exercise intolerance, he will not be able to continue at that level of work.

Types of Surgical Treatments for Roarers

Laryngoplasty or laryngeal prosthesis is the current standard surgical treatment for horses with Grade IV laryngeal hemiplegia. This can be performed under general anesthesia or standing while sedated. This procedure involves tying back the paralyzed cartilage into an abducted or open position. This procedure is often referred to as tie-back surgery in horses.

Often the ventricle and vocal cord (ventriculectomy/cordectomy) which are located under the arytenoid cartilage are removed to help widen the airway. This procedure can be done in conjunction with the laryngoplasty or alone. In horses that do not need to perform at high speeds, it can improve performance and reduce the noise by allowing better airflow. This procedure is usually recommended in horses exhibiting Grade IV laryngeal hemiplegia along with laryngoplasty.

Horses suffering from Grades II and III may be able to function normally without surgical treatment and only management changes. There have been reports of some of these horses being treated successfully with acupuncture.

Post-Surgery Care and Recovery

Postoperative care following laryngoplasty involves treatment with antibiotics and anti-inflammatories. Recovery usually includes 30 days of stall rest with hand walking or grazing. This is then followed by turnout in a small paddock or light exercise for another 30 days. It will usually take 45-60 days before the horse is able to return to normal exercise.

Horses that only had a ventriculectomy or cordectomy will need twice daily cleaning of the surgical site and hand walking or small pasture turnout until the surgical site has healed (this takes about 30 days).

Recovery and Prognosis for Roarers

The prognosis for horses returning to normal activity post-treatment is good. Horses used for showing and jumping have a 90% chance of returning to their previous level of performance, while racehorses have approximately a 60-70% chance of returning to their previous level. Older horses can respond more favorably to treatment than younger horses (two-year-olds).

Of course, there can be complications from laryngoplasty surgery, which include:

  • continued exercise intolerance and the roaring noise
  • chronic coughing, caused by the inability of the left arytenoid to close, thus failing to protect the airway from aspiration of food and water
  • loosening of the prosthetic sutures
  • loss of complete abduction of the arytenoid

Managing a Horse Who Roars

Maintaining respiratory health in horses is extremely important in preventing respiratory illness and helping your horse maintain long-term performance goals. It is always smart to keep horses in a low-dust, well-ventilated environment. Horses that have had laryngoplasty may benefit from having their hay soaked. A respiratory supplement with antioxidants that targets tissues of the airway, such as Vitamin C and N-Acetyl Cysteine, may be of benefit.

Questions Owners Commonly Ask the Vet About Roaring

Can you ride a horse that roars?

Yes. However, care and attention must be taken so you do not exert the horse and compromise or impair their breathing.

Would you buy a horse that roars?

The answer depends on the proposed use of the horse. If you’re looking to buy an upper-level jumper, dressage mount, eventer, barrel racer, or racehorse that requires maximum exertion for sustained periods, purchasing the horse would probably be discouraged.

Can you fix a horse that roars?

In many cases, tie-back surgery or other surgical treatments are successful. There are new treatments being studied (such as nerve regeneration and transplants) that also may prove to be successful in the future.

Is roaring in horses a progressive condition?

Whether roaring is progressive usually depends on the cause. Traumatic damage to the left recurrent laryngeal nerve will usually be relatively immediate. In horses exhibiting a Grade II or III roar, it may progress to a Grade IV over time. It is before it reaches Grade IV that treatments using acupuncture and nerve regeneration are most successful.

SmartPak strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.