This is a spasmodic upward jerk of the limbs during progression. It is chiefly observed in the hind extremities, but rarely also affects the fore ones.
In the former it is marked by a convulsive flexion of the hock, when the canon is raised high up towards the abdomen, with which it is on occasions brought into contact. This disordered movement may affect one or both hind-legs equally, or in different degrees.
It is almost exclusively confined to the walk and the trot, and varies from time to time in the suddenness and extent of the morbid movement. It is exaggerated after rest, and also by excitement. In many instances horses are taken to shows which while at home are perfectly free from the defect, but which no sooner get into the show ring than they develop stringhalt in a very marked form.
In some animals it is very slight, and only observed in turning. In others it is intermittent, and only seen now and again. Hackneys, whose hock action is now so much developed, are more frequently affected by it than any other variety of the horse.
Stringhalt has been attributed to a variety of causes - some anatomical, others pathological - and it has been variously located in the stifle, the hock, and the pastern, and attributed to laceration of muscles of the thigh, to rupture of the tendons inserted into the point of the hock, and to ulceration of joints. In this country it is pretty generally regarded by veterinarians as a nervous affection, but the proof of this, as of all other alleged causes, is still wanting.