Laryngeal Hemiplegia in Mules: Roaring, Noise, and Exercise Intolerance

Laryngeal hemiplegia is a disorder of the upper airway in which one side of the larynx does not open normally during inhalation. In equids, it is usually the left side that is affected. The problem happens when the recurrent laryngeal nerve and the muscles it controls weaken over time, so the arytenoid cartilage and vocal fold cannot abduct well enough to keep the airway open during work.

As airflow speeds up, especially during exercise, the weakened side can collapse inward. That creates the classic harsh breathing noise many people describe as roaring. It can also reduce airflow enough to cause poor stamina, slower recovery, and reluctance to keep working.

Most of the published veterinary information is in horses, but the same airway anatomy and disease process apply to mules. In practice, your vet will usually approach a mule with roaring and exercise intolerance much like an equine recurrent laryngeal neuropathy case, while also considering the mule's job, temperament, and handling needs.

Not every mule with this condition needs the same plan. Some do well with monitoring and lighter work. Others, especially athletic or working animals that need strong airflow, may need a more involved diagnostic workup and discussion of surgical options.

The usual cause is degeneration of the recurrent laryngeal nerve, the nerve that activates the main muscle responsible for opening the larynx. As that nerve loses function, the muscle atrophies and the airway cannot stay as open as it should during inhalation. In equids, the left side is affected most often because the left recurrent laryngeal nerve is much longer.

In horses, this condition is often grouped under recurrent laryngeal neuropathy. Published sources describe it as more common in larger, long-necked equids and more common on the left than the right. Those same principles are useful when your vet evaluates a mule, even though mule-specific prevalence data are limited.

Less common causes include direct trauma to the nerve, complications from injections of irritating substances in the neck region, and certain toxic exposures. Bilateral laryngeal paralysis is uncommon and raises concern for broader neurologic or toxic problems.

For many individual animals, there is no single event pet parents can point to. That can be frustrating, but it also means the next step is usually not guessing at the cause. It is confirming how much the airway is affected and matching treatment to the mule's daily work and breathing needs.

Diagnosis starts with a history and physical exam, including when the noise happens, what kind of work triggers it, and whether stamina has changed. Your vet may listen to the airway after exercise and look for other causes of poor performance, because roaring is not the only reason a mule may tire early.

The key test is upper-airway endoscopy, ideally performed while the mule is unsedated. This lets your vet watch the arytenoid cartilage and vocal fold move in real time. Equine specialists commonly use a grading system to describe severity. If the resting exam is borderline or the signs only happen during work, your vet may recommend dynamic endoscopy during exercise to see whether the airway collapses more under load.

In some cases, laryngeal ultrasound helps support the diagnosis by showing muscle changes consistent with nerve dysfunction. Your vet may also discuss other conditions that can mimic this problem, such as arytenoid chondritis, nasopharyngeal collapse, or other upper-airway disorders.

Typical 2025-2026 US cost ranges are about $250-$600 for an exam plus resting upper-airway endoscopy, and roughly $500-$1,200 when dynamic endoscopy, sedation, farm call, or additional imaging are added. Referral-hospital costs can be higher.

There is no guaranteed way to prevent laryngeal hemiplegia because the most common form is related to nerve degeneration rather than a simple management mistake. Still, early recognition can prevent a mild problem from becoming a major work-limiting issue before your vet evaluates it.

Pay attention to new exercise noise, reduced stamina, slower recovery, or reluctance during harder work. Keeping notes or short videos of when the noise happens can help your vet decide whether a resting exam is enough or whether exercise endoscopy would be more useful.

Good general airway health also matters. Work your mule at an appropriate fitness level, avoid pushing through obvious breathing strain, and ask your vet to evaluate any persistent cough, nasal discharge, or poor performance rather than assuming it is training related.

If your mule has already been diagnosed, prevention shifts toward preventing flare-ups and complications. That may mean adjusting workload, avoiding extreme exertion in heat, following postoperative instructions carefully if surgery is performed, and scheduling rechecks if breathing noise or exercise intolerance changes.