Page 249 - The Veterinary Care of the Horse

heels are said to be underrun. The altered hoof angle affects the normal blood flow

through the hoof.
VetBooks.ir • The weight of the horse is shifted backwards and may cause the horn tubules of the heels

to be crushed and collapse forwards.
• The front feet gradually lose their round shape and become more oval when viewed from

the ground surface.
• As the hoof elongates, the heels become contracted.

• Lameness may result from:

– increased tension on the deep digital flexor tendon and the navicular ligaments;

horses with this type of conformation are susceptible to developing navicular
syndrome and they often have heel pain

– strain of the superficial digital flexor tendon

– tearing of the laminae at the toe because the long toe and altered hoof angle
increase the breakover time and impose increased strain on this area.

Figure 6.38 Underrun heels: a) normal hoof with parallel alignment of hoof tubules; b) underrun heel

Breakover is the phase of the stride that starts when the heel begins to lift from the ground

and ends when the toe leaves the ground. During breakover, the hoof rolls about 45 degrees.
The point of breakover is the furthest-forward part of the foot or shoe that is in contact with

the ground when the heel begins to lift.
Long toes in the hind limbs may lead to hock and back pain. Radiographs of affected hind

feet sometimes reveal that the orientation of the pedal bone within the foot is abnormal. The
lower border of the pedal bone may become parallel with the ground surface or even tilted so

that the toe of the pedal bone is higher than the heel area (rather than the normal 2–10 degree
angle with the ground surface, and the back of the pedal bone slightly higher than the front).