Page 707 - The Veterinary Care of the Horse

degenerative changes in some horses. The muscles supplied by the damaged nerve waste

away and the left side of the larynx is no longer capable of the normal range of movement.
VetBooks.ir There is incomplete opening of the left side of the larynx resulting from loss of function of
the dorsal cricoarytenoid muscle. During fast exercise the flow of air is obstructed (Figure

15.21).

Figure 15.21 A normal and a paralysed larynx

The right recurrent laryngeal nerve is rarely affected. Neuropathy of the right recurrent

laryngeal nerve is a rare and unfortunate consequence of intravenous injections given on the
right side of the neck where some of the drug is accidentally deposited outside the vein.

Clinical signs

• The horse makes an abnormal noise when it breathes in at canter and gallop. This is due
to turbulence in the air stream as the air passes through the obstructed laryngeal opening.

The tissue on the affected side vibrates and causes a noise. It may be a high-pitched
whistle (in mild cases) or a harsh roaring sound. In severe cases it can be heard at trot.

The noise should not be confused with normal expiratory (breathing out) sounds such as
‘high blowing’ which is caused by air turbulence at the nostrils.

• The horse may show reduced performance at exercise as the tissues receive less oxygen.
• The horse’s voice may change.

• As the muscles on the left side of the larynx atrophy (waste away), the process on the left

arytenoid cartilage where the wasted muscle attaches becomes more prominent and may