What Is Roaring in Horses: Causes and Treatment

Roaring is the harsh, rasping noise some horses make as they breathe in at speed. It comes from a partly paralyzed voice box that narrows the airway. The noise is what owners notice, but the real problem for a working horse is that less air gets in just when it’s needed most. It’s a common, well-understood condition, and there are treatments that let most affected horses go back to work.¹

What Happens Inside a Roaring Horse’s Throat

Vets call roaring laryngeal hemiplegia, or recurrent laryngeal neuropathy (RLN), terms you may see on a vet report. It means one side of the voice box is paralyzed because of a nerve problem.² The nerve that supplies the muscle responsible for pulling the voice-box flap open slowly loses its largest fibers.³ That flap ends up partly or completely paralyzed, almost always on the left side.⁴ The damage starts at the far end of the nerve and creeps backward, and in severe cases the right nerve can be affected too.⁵

In a healthy throat, that muscle contracts with each hard breath and swings the flap, and the vocal cord attached to it, out to the side. This gives air the widest possible channel. When the muscle has wasted from loss of its nerve supply, nothing holds the flap out against the suction of the in-breath, so it is drawn toward the middle of the airway. The opening narrows, and air squeezing through becomes turbulent. That turbulence is the source of both the sound and the extra effort.

Speed is what exposes it. Airflow through a horse’s upper airway can climb from about 240 litres a minute at rest to about 4,500 litres a minute at full gallop.⁶ That creates huge pressure swings in the airway, which suck weak tissue inward.⁷ A flap that hangs loose barely matters when the horse is standing still, but at speed it collapses into the airway, causing turbulence and noise and making the horse tire early.⁸

The noise is heard on the in-breath. It usually gets louder as the horse speeds up and fades quickly once it stops. At a walk or at rest, most roarers sound completely normal. Some horses also whistle, which comes from the vibrating vocal cord.

Loudness is a poor measure of how much a horse is struggling, because the noise depends partly on how the loose tissue vibrates and not only on how narrow the opening is. One horse can make a lot of noise yet keep working well, while another with a quieter throat tires early. The signs of a real performance problem are running out of steam late in a race or hard session, or slowing sooner than horses of similar fitness.

The problem is also progressive. Nerve fibers are lost gradually, so a mild case can worsen over months or years, and a horse that sounded quiet as a youngster may start roaring later.

Why the Left Side and Why Big Horses

The left nerve loops down around the base of the heart before coming back up to the voice box, which makes it much longer than the right.⁹ A long nerve is more prone to failure,¹⁰ so bigger horses with long necks are more likely to develop roaring.¹¹ In Thoroughbreds, horses with roaring tend to be taller at the withers, have longer necks, and be older.¹²

Because the fibers fail from the far end first, the longest nerve has the most length in which something can go wrong. The right nerve is shorter and takes a direct route, so it is rarely affected on its own, and when it is involved it usually means the disease is advanced. The same pattern explains why the condition turns up in tall breeds beyond Thoroughbreds, including draft horses.

Genes play a large part too. In Thoroughbreds, roughly half the risk is inherited by one genetic estimate.¹³ The genes that make a Thoroughbred tall appear to be almost the same ones that raise roaring risk,¹⁴ and researchers have found genetic markers linked to the condition.¹⁵

Less often, the nerve is damaged by direct injury, a guttural pouch problem, or an irritating drug accidentally injected outside the jugular vein.¹⁶ Poisoning from certain plants such as chickpeas and Lathyrus peas, or from chemicals, can also cause it.¹⁷

Height, neck length and genes are fixed, so nothing in feeding or training prevents typical roaring. The rarer causes are more controllable: careful injection technique in the neck avoids one, and keeping horses away from Lathyrus peas or chickpea feed avoids the toxic one. Roaring that appears suddenly after a neck injury or illness points to one of these rarer causes and needs a vet.

A tall, long-necked horse is more likely to be at risk, though many such horses never roar, so size alone is not a diagnosis. A parent that roars raises the odds for its foal without guaranteeing it.

How Roaring Affects Breathing and Performance

Roaring does real harm beyond the sound. During hard exercise, roaring horses end up short of oxygen, with too much carbon dioxide and acid in their blood compared with normal horses.¹⁸ In one horse, oxygen in the blood after a mile of fast work rose from about 53 to about 84 mm Hg after surgery.¹⁹ Breathing through a narrowed airway costs the horse more energy just to breathe.²⁰ Surgery improves these values without bringing them fully back to normal.²¹

A galloping horse takes roughly one breath per stride, so it can’t simply breathe more often to make up for a narrow airway. Low oxygen and high carbon dioxide make muscles tire sooner. Horses with mild roaring may only show this at the very top level of effort.

How much it matters depends on the job. A racehorse or eventer working flat out feels the oxygen shortage most, while a pleasure or light hacking horse may never be held back. Noise alone can still count against a horse in show classes or at a sale.

How Vets Diagnose and Grade Roaring

A camera scope passed down the nose shows how well the flap moves. Vets score it on the Havemeyer grade, which is used to guide treatment choice.²²

The horse usually stands lightly restrained or sedated. The vet watches how the flap moves, sometimes asking for a swallow or briefly closing the nostrils to prompt a bigger breath. Sedation can change how the flap moves, so the vet takes that into account when reading the result.

A resting scope is a useful start, since grade at rest is linked to collapse at exercise.²⁷ But about 1 in 5 horses with a grade 3 or 4 score at rest still opened fully during hard work,²⁸ and about 7% of horses rated normal at rest showed collapse when worked.²⁹ Grade can vary between exams, and some problems only appear at speed.³⁰ Before surgery or a big purchase decision, an exercise scope, on a treadmill or with a riding-mounted scope, gives the clearest answer.

An overground exercise scope uses a thin camera fitted through the nose and held in place by the bridle. The horse is ridden or driven at its normal working speed, and the vet watches the video live or afterwards for collapse. It’s well tolerated, with few complications.

A scope also separates roaring from other noises. A soft palate that slips out of place causes a gurgling noise, not a roar, and several throat problems can occur in the same horse. Describing the noise alone misdiagnoses many horses.

A pre-purchase scope is a snapshot, not a guarantee for the horse’s career. Someone buying for hard work should ask whether the grade fits the horse’s job and whether an exercise scope was done. If a horse already has a documented grade 3 or 4, the next question is whether it collapses at exercise, since rest grade doesn’t always predict it.

Treatment Options for Roaring

The nerve damage doesn’t heal with time off, and medications don’t restore the muscle. Treatment manages the airway rather than reversing the disease.

The tie-back (laryngoplasty) uses a strong suture to pull the paralyzed flap open permanently.³¹ The surgeon makes a cut in the neck and places the suture around the flap, anchoring it to a cartilage of the voice box so the flap is held open. The aim is to improve airflow without opening it so far that swallowing is compromised, so the surgeon is balancing two risks. The horse is under general anesthesia. The tie-back is the treatment of choice for horses that tire because of roaring.³² In some horses the flap slips back partly after surgery, and surgeons are still refining suture methods to hold it.³³

Vocal cord surgery removes the vocal cord and the small pouch behind it, and it mainly quiets the noise.³⁴ In draft horses, 83% of owners felt the noise improved enough to compete after this surgery.³⁵ Done with a laser through a scope, 91% of horses returned to their intended use and noise stopped in 82%.³⁶ It can be done safely in a standing, sedated horse.³⁷ In more severe cases, collapse of the right side can remain after the left vocal cord is removed.³⁸

Because the flap isn’t held open, the airway isn’t widened much, so this surgery is chosen when quiet matters more than extra airflow. It is often done on its own for horses whose work isn’t very demanding, or alongside a tie-back so one surgery tackles both noise and airway size.

A nerve-muscle graft moves a healthy nerve from the neck into the paralyzed muscle to bring it back to life.³⁹ Success rates are similar to the tie-back, and it can take up to a year to work.⁴⁰ That makes it a fit for a horse that can wait months before full work.

A noisy horse that isn’t tiring may only need vocal cord surgery, while a racehorse short of air usually needs a tie-back, often combined with vocal cord surgery. What an exercise scope shows, along with the horse’s job, helps decide which.

Useful questions for the surgeon: is the goal quieter breathing or better performance, since the two operations aim at different things? Was an exercise scope done, and what does the surgeon expect the grade and the tiring to look like afterward? And what is the surgeon’s own experience and complication rate with the operation, since technique varies between surgeons?

Recovery and Return to Work

After surgery, 96% of racehorses in one group returned to racing.⁴¹ Return took a median of about 7 months.⁴² Only about half of the horses that raced before and after showed better results,⁴³ though of those with at least three starts on each side of surgery, 75% improved.⁴⁴ Some horses were already running well with a mild problem, leaving less room to improve, which is one reason the share who improved was lower than the share who returned.

After a tie-back the horse typically has stall rest first, then a slow build-up of walking and then ridden work, with the surgeon setting the timetable. Rushing back to hard work risks stressing the repair before the neck has settled. Plan for months, not weeks.

A repeat scope helps confirm the flap is holding. Other airway problems can still limit a horse after a successful tie-back, and many horses still make some noise even when breathing better.

Complications to Watch For After a Tie-Back

Lasting coughing and difficulty swallowing are fairly rare after a tie-back.⁴⁵ They’re most common when the flap is pulled open too far, leaving the airway less protected during swallowing.⁴⁶ Normally the flap and its neighbors help close off the windpipe when the horse swallows, keeping food and water on the right route. With the flap held too far open, some food or water can slip into the windpipe.

Affected horses cough while eating and often have feed coming out of the nose.⁴⁷ At home, watch for coughing during feeding in the first days or weeks, and for food or green discharge from the nostrils. Ask the vet whether feeding hay from the ground would help. Fixes are easier soon after surgery, so call early.

The vet will usually scope the throat to see how the flap is sitting and whether the swallowing difficulty is explained by its position or by something else. Early care includes antibiotics and anti-inflammatory drugs.⁴⁸ Some surgeons loosen the suture within days, or remove it later, and swallowing problems resolved after removal.⁴⁹ A filler injected into the vocal fold cleared the problem in 80% of horses and improved the rest, and 94% returned to work.⁵⁰

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