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September 16, 2009

Helping Roarers Breathe Easy

Horsemen can get caught up in the specifics of their disciplines, but the basic needs of sport horses, like all athletes, are simple: water, food and air.

The act of breathing, so commonplace that it’s often taken for granted, is of such importance in equine athletes that race horses with one tiny misalignment in the upper airway can immediately be destined for a different career.

“Roaring,” formally known as left laryngeal hemiplegia, is an upper airway obstruction that occurs when a horse suffers from paralysis or weakening of one of the crucial structures in his throat.

As the name indicates, horses with a roar often exhibit raspy or wheezy breath during strenuous exercise. Although the disease can be traced back to a nerve issue, the noise is essentially caused by a piece of cartilage flapping in the horse’s airway instead of pulling back properly to allow for the maximum flow of oxygen during exercise.

The disease is considered idiopathic, meaning vets aren’t usually sure why some young horses, especially Thoroughbreds and draft horses, are stricken with it.

For years, the only fix has been a surgical procedure, formally known as laryngoplasty but commonly called tie-back surgery, to literally “tie back” the offending cartilage. The goal: eliminate the noise and make sure horses can get a normal amount of air during periods of intense exercise.

These days, advances in medicine are opening the door for better surgical procedures to treat roaring. A few years ago, Eric Parente, an associate professor of surgery at the University of Pennsylvania’s New Bolton Center, pioneered a process of fusing a joint in the throat to increase the success rate of keeping the airway open.

“One goal we have is to better understand the cause of the disease and the biomechanics of the disease so we can figure out the best way to correct it,” said Parente. “It’s like, before you build a better mousetrap, you have to know how big the mouse is.”

Parente is working on an even better procedure to treat roaring, but that procedure is too new to discuss yet. Meanwhile, other researchers and surgeons are experimenting with laser surgery to zap off the other, smaller pieces of tissue that cause only the noise in a horse’s throat. Tie-back surgery, which requires full anesthesia, aims to eliminate the noise and the entire airway obstruction.

Another procedure involving nerve grafts is also getting some attention, but the success rate of that technique is not as high as some of the other more traditional procedures, Parente said.

The Cause Of The Noise

Although roaring is most often seen in Thoroughbreds and draft horses, it’s now being diagnosed in more warmbloods, said surgeon Courtney Bollam at the Wisconsin Equine Center Clinic in Oconomowoc.

According to the New Bolton Center, non-race horses make up about 15 to 20 percent of the horses afflicted with the disease. The disease is usually noticed in horses when they are 2 or 3. Occasionally, trauma to the neck such as a sharp kick or a misplaced intravenous injection can cause the condition. An endoscope is used to diagnose a roarer, and horses are rated on a scale to rank their severity.

Internally, the problem is a paralysis of one of two arytenoid cartilages in the throat. Almost always, the left cartilage is the one that fails to work properly.

You may need a brief review of a horse’s upper airway anatomy to understand the importance of these two cartilages, which are about the size of silver dollars. When horses breathe, air goes up the nasal passages and over the soft palette before crossing the pharynx and entering the trachea, or windpipe. From there, air enters the larynx, or voice box.

Because food and water need to stay out of the “pipe” used for breathing, the larynx is guarded by a valve system: the strong epiglottis tissue, and a pair of arytenoid cartilages that form a “V” at the opening of the larynx.

When a horse swallows, the epiglottis and arytenoid cartilages seal off the larynx from the incoming substances. During exercise, the arytenoid cartilages work in reverse, pulling back wide and open to allow maximum oxygen to reach the working horse.

In horses that roar, one of those pieces of cartilage gets weak, and the dangling arytenoids flap flutters, causing that wheezy, raspy noise that will likely result in markdowns if a judge hears it on course in the hunter arena.

In addition to the unpleasant sound the arytenoid cartilage can get in the way of the horse receiving a normal amount of oxygen, resulting in fatigue or “exercise intolerance.”

The root cause of the problem is a nerve issue. In a healthy horse, the arytenoid cartilages are activated by a particular muscle, which moves the cartilage back and forth. But in horses with a roar, that muscle has weakened because the nerve that sends the signal to that muscle isn’t functioning properly.

Some vets theorize that the nerve has a tendency to malfunction because unlike most nerves, which run straight from the brain to the location of the body they’re tasked with serving, the nerve serving the muscle that moves the arytenoid cartilages runs from the brain, down the neck, turns around, then comes back up the neck to the throat.

The long, circuitous route means the nerve may be prone to impulse malfunctions in the same way that long rubber garden hoses have a greater tendency to kink than short hoses.

“Most nerves go from A to B, not from A, down around the block, around the corner and back up to B,” said Bollam.

Repairing The Damage

To correct that muscle’s failure to perform its job, tie-back surgery involves placing one or two permanent sutures on the side of the larynx to pull the loose cartilage halfway between open and closed. Some surgeons, like Parente, prefer to pull the cartilage back so that the airway is about 80 to 90 percent open.

Eventually, scar tissue that forms around the suture forms a “scaffold” of extra reinforcement for the area, said Bollam.

“We can see the weakened arytenoids up their nose as we tie up the suture,” Bollam said. “It’s a fairly technical surgery; we make the incision that’s about 8 to 12 inches long on the underside of the jaw, at the beginning of the neck.”

It’s uncommon for the suture to break after surgery, but it can pull through the muscle and cartilage.

Complications also arise when the tie-back simply fails to keep the airway open wide enough. Because horses that have had tie-back surgery have to learn to swallow food and water without aspirating, many develop a chronic cough.

“The No. 1 complication is maintaining the opening where you want it,” said Parente. “The No. 2 complication is aspiration.”

In Parente’s fusion technique, in addition to putting in two sutures, he locates a small joint, the cricoarytenoid joint, between the two cartilages and fuses it in the open position. He’s extremely careful to get the opening in exactly in the right place before he fuses the joint, he said.

The technique addresses his No. 1 complication, but it still requires horses to learn how to swallow food in a new way without aspirating any of it. The joint takes several weeks or a month to fuse completely.

Parente said the clinic is currently doing a retrospective study of 200 to 300 horses that have had the fusion technique to see if it does indeed hold up better over time than the sutures alone.

For some horses, especially draft horses that can’t always withstand hours of general anesthesia, veterinarians can also use a laser, with the assistance of an endoscope, to remove small pieces of tissue that impede the flow of air and create noise.

“It depends on what the owner’s goals are,” said Bollam. “If exercise intolerance isn’t the main issue, and the noise is the real problem, we can do just the ventriculectomy in 5 minutes while the horse is standing. The small incision under the jaw is left open, and it heals on its own.”

The price difference between the standing procedure and major surgery is substantial. A ventriculectomy may only cost around $700 or $800, while the price of a laryngoplasty may cost $2,000 to $2,500 with hospitalization and post-operative care. And surgery doesn’t always eliminate the noise completely.

Often times, however, if the horse is already going down for the laryngoplasty, the surgeon will perform the ventriculectomy, or a similar procedure called a ventriculochordectomy as well. Others perform one of those procedures with the laryngoplasty but a day apart.

“I think I can do a better job, and do it faster, while the horse is out,” said Parente, who usually recommends clients agree to the tie-back surgery combined with the ventriculochordectomy.

A less-used technique is equine laryngeal reinnervation (nerve supply) surgery. The procedure involves grafting pieces of working nerves onto the faulty nerves that are supposed to move the arytenoid cartilages. Formally, the procedure is known as a “neuromuscular pedicle graft.”

Parente isn’t hot on the procedure, which he said only has about a 50 percent success rate. Because it takes a long time to see if the procedure worked, many people still prefer to try the other more traditional techniques for roaring. If there’s no sign of improvement after 12 months of reinnervation, most of those horses end up having to have tie-back surgery anyway.

Meanwhile, Parente said he’ll keep looking for more effective methods of treating the disease.

“Our success rate is great for 70 to 80 percent of horses,” he said. “That’s not enough for me. Until we can get 100 percent, I think we need to keep looking for better techniques.”

 

 
Horse lovers dating
4 years 32 weeks ago
Most often a horse will give
Most often a horse will give some indication that a rear is coming, allowing you some split seconds to plan what you can do to avoid the behavior. Dating for horse lovers Before anything else... Read More

Comments

Horse lovers dating
4 years 32 weeks ago

Most often a horse will give

Most often a horse will give some indication that a rear is coming, allowing you some split seconds to plan what you can do to avoid the behavior. Dating for horse lovers Before anything else consider physical problems.

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