The terms ‘whistler’ and ‘roarer’ are used to describe horses which make an abnormal respiratory noise during exercise. The noise is heard during inspiration (i.e. breathing in) and may be anything from a high-pitched soft whistle to a harsh ‘roar’.
What causes the noise?
With each breath, air is taken in through the nostrils and passes via the nasal passages to the throat (pharynx), which is a dynamic and muscular tube. From here it passes through a cartilaginous valve, the larynx (voice box), before entering the windpipe (trachea) and lungs. During exercise, the nostrils dilate and the horse extends its head and neck, further opening the pharynx and larynx to take in more air. Anything which interferes with the smooth passage of this increased air flow may result in the horse making an audible noise.
Laryngeal hemiplegia (one-sided paralysis) is the most common cause of horses making abnormal noises during inspiration at fast exercise. The noise is caused by partial or total paralysis of one (usually the left) side of the larynx (voice box). It occurs mainly in larger horses, because it is thought that this conformation can predispose to injury to the long nerve (recurrent laryngeal nerve) which motivates the left side of their larynx. Nevertheless, it can be seen in smaller horses and ponies.
In mild cases the noise may only be heard during strenuous exercise but in severe cases the noise might be evident during trotting. Exercise intolerance (i.e. getting tired quickly) can be a problem as the horse has difficulty getting enough air through the incompetent larynx. The disease is progressive and gets worse with time. In a severely paralysed larynx, the airway actually gets smaller rather than bigger during strenuous exercise as the paralysed side collapses inwards.
How can the diagnosis be confirmed?
Laryngeal hemiplegia is usually diagnosed firstly by listening to your horse exercising to detect either normality or an abnormal inspiratory noise. Next the horse should undergo an endoscopic examination, i.e. a flexible periscope-type instrument is passed through the nose, into the pharynx, to look at the larynx as the horse breaths. Both sides of the larynx should open and close in synchrony, almost symmetrically and completely. In the horse with laryngeal hemiplegia, usually the left side of the larynx moves sluggishly and incompletely, ‘hanging’ into the larynx and obstructing airflow during inspiration. In some difficult cases, it may be necessary to have an endoscopic examination performed while the horse is exercising on a high-speed treadmill, in order to make the diagnosis. The treadmill has now been superseded by "overground endoscopy". This consists of a camera inserted up the horses nose and secured to the bridle. A pack on the riders back transmits a signal to a monitor allowing the larynx to be visualised while the horse undergoes its normal excerise.
What treatment is available?
Horses used for hacking or less strenuous jobs can cope without treatment. It is important to keep their respiratory tract healthy from infections and allergies with good management (i.e. low dust, good ventilation, proper vaccination regime etc.).
In moderately severe cases, it may help to do a ‘Hobday’ operation in which a piece of laryngeal tissue (laryngeal saccule) is surgically removed to encourage a scar to form to ‘tighten’ the larynx in a more open position. In more severe cases a ‘tie-back’ operation is often recommended. This more elaborate operation places sutures in the paralysed side to pull and hold it open. The ‘Hobday’ operation is often performed at the same time so that the resulting scar also helps to hold the paralysed side open, even if the sutures fail to retain their strength over time. In horses where a tie back has failed or is not an option for other reasons, a brass or plastic tracheotomy tube may be inserted into the windpipe to allow air to bypass the larynx completely. The tracheotomy tube and wound must be carefully managed to prevent infection and secondary complications and this method is very invasive and many people understandably find it unacceptable for aesthetic reasons.
What other conditions cause whistling and roaring?
There are several other conditions which may cause a horse to make an abnormal inspiratory noise.
- Lymphoid hyperplasia is a term used to describe a condition where lymphoid (immune) tissue lining the pharynx becomes inflamed and nodules form. It is a condition affecting young horses and most cases improves with age.
- Cysts (fluid-filled sacs) may form beneath the epiglottis. The epiglottis is a triangular cartilage at the base of the larynx. Its job is to prevent food material from going down ‘the wrong way’ i.e. down the windpipe. If a cyst forms under it, the epiglottis is pushed up and it obstructs the opening of the larynx causing a noise. Large cysts require surgical treatment to remove them.
- Infections, tumours etc. in the nostrils or nasal passages may result in the horse making an abnormal noise.
- Epiglottic entrapment is a term used to describe a condition where the epiglottis is trapped under an abnormal fold of tissue and cannot move normally. Treatment consists of cutting the abnormal tissue, for which a surgical procedure is required.
- Congenital problems are conditions of the pharynx and larynx which are present from birth. In general terms, these conditions cannot be treated.
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Clyde Vet Group advises that you should always consult a veterinary surgeon about any queries with animals under your care.