Page 484 - The Veterinary Care of the Horse

Degenerative changes in particular nerves are associated with stringhalt but the cause of these

changes is unknown. There are two forms of the disease. ‘True’ or ‘classic’ stringhalt occurs
VetBooks.ir worldwide as isolated cases and a suggested cause is trauma to the front or lateral aspect
(outside) of the hock or the upper cannon bone. Back or neck injuries are other possible

causes.

The second form of the disease occurs mainly in Australia and New Zealand. Groups of
horses grazing together may be affected. It tends to occur on poor pasture in summer or
autumn in fields with toxic weeds following a long, dry spell of weather. Flatweed,

Hypocheris radicata has been implicated. This plant has green leaves in a rosette form, with
small dandelion-like flowers on a long stem. It is likely that other, as yet unknown, factors

are also involved eg mycotoxins and environmental conditions.
The Australian form of the disease is more severe. It is often bilateral and may affect the

forelimbs and the muscles of the larynx as well.

In either form, the cause of the jerky hyperflexion of the hock joint is not understood.
Altered sensation or muscle reflexes as a result of the nerve degeneration may be responsible.

The long and lateral digital extensors are two of the most affected muscles.

Treatment

• Horses mildly affected by classic stringhalt may be able to perform their work with no

treatment.
• Severely affected horses may improve after an operation to remove part of the lateral

digital extensor muscle and its tendon.

• With the Australian stringhalt, the first step is to remove the horse from the pasture.
Good nutrition with balanced minerals and vitamins is important for normal nerve

function. Some horses will recover spontaneously over 6–12 months, although others
may take up to 3 years. A drug called phenytoin which is normally used as an

anticonvulsant may help these horses owing to its action on nerves and muscles.
• Muscle relaxants may result in a temporary improvement but along with anticonvulsants

have sedative side effects.
• New research using botulinum toxin (Botox) to suppress stringhalt symptoms is showing

promising results.

Prevention

Prevention of classic stringhalt is not possible as the cause is not known. With the Australian