Roaring is a condition that causes some horses to make a whistling or roaring sound during exercise. It can affect a horse’s performance during high-intensity exercises, such as racing.

This condition is also referred to as recurrent laryngeal neuropathy (RLN) or laryngeal hemiplegia. It is estimated that 2-8% of Thoroughbreds and up to 35% of draft breeds are affected by RLN. [1]

The larynx is part of the trachea (windpipe) and includes the vocal cords. RLN involves the partial collapse of cartilage in the larynx caused by progressive weakening of nerves.

This narrows the space that air passes through while the horse is breathing, causing a characteristic roaring noise, especially under heavy work. [2]

The condition is usually first noticed when the horse starts training around 2-3 years of age. In hunting and sport horses, laryngeal hemiplegia may not be noticed until around the age of seven. [3]

Early and frequent monitoring of laryngeal function in affected horses is important to determine whether surgical intervention is necessary or whether the horse should be retired from exercise.

If your horse is roaring, you can support their respiratory health through good nutrition and management to improve oxygen delivery and exercise tolerance.

The Equine Larynx

The larynx is the narrowest portion of the horse’s upper airway. It starts at the back of the mandible (jaw bone) and extends down into the neck.

The larynx serves as a channel between the pharynx and the trachea (windpipe). It transports inhaled air to the lungs for gas exchange. [18]

The intrinsic laryngeal muscles are involved in respiration, phonation (vocalization) and protecting the airway.

In horses with laryngeal hemiplegia, the left recurrent laryngeal nerve that controls the laryngeal muscles is damaged. In rare cases, the right laryngeal nerve is also affected.

The left recurrent laryngeal nerve loops around the horse’s aorta while the right takes a shorter route around the right subclavian artery. The left nerve can be up to 250 cm long – twice as long as other motor nerves in the horse’s body.

It is this length and the complexity of the left recurrent laryngeal nerve that likely puts it at risk of pathological changes that cause roaring. [4]

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Recurrent Laryngeal Neuropathy

RLN is usually caused by damage to the left recurrent laryngeal nerve, leading to a loss of nerve supply in the laryngeal muscle. This results in muscle atrophy within the larynx.

In healthy horses, the laryngeal muscles pull on (abduct) the aryteoid cartilage of the larynx to open the airway for inhalation. Following exhalation, the muscles relax and the airway closes slightly.

In horses with RLN, there is incomplete abduction of the arytenoid cartilage and vocal cord. Instead, these structures collapse into the horse’s airway during exercise.

This results in abnormal and often loud breathing noises, best described as a “roar”.

RLN also leads to increased respiratory resistance, a reduction in airflow, and a low concentration of oxygen in the blood (hypoxemia). [5]

Damage to the left recurrent laryngeal nerve (and sometimes the right) can also lead to total or partial paralysis of the larynx. [6]

Causes of Roaring

For the vast majority of RLN cases, the trigger leading to the development of the condition is unknown. [6]

However, there have been documented cases of laryngeal paralysis caused by:

  • Injury to the right or left r