WHAT MAKES A GOOD HOOF?
Most people can identify a hoof that has superficial damage, for example overdue for shoeing or has cracks in the hoof wall. But the trouble is that we don't understand how to assess the internal health of a hoof. To do this you need to examine the digital cushion. Heres how...
Make fist and squeeze the thumb muscle - it feels firm.
Next relax your hand, squeeze the thumb muscle again - it feels soft.
Now you can squeeze the back of the horses foot and see how the digital cushion feels - firm and elastic, or soft and squishy.
You need to feel lots of feet, including healthy hard working barefeet, to develop an idea of good and bad.
WHY IS THIS A GOOD INDICATOR OF HOOF HEALTH?
The digital cushion is a crucial shock absorbing structure. If it is weak it is not able to perform this function and the horses weight impacting on this area is painful. This will cause the horse to place his feet on the ground toe first rather than heel first. The toe wall is fairly rigidly attached to the pedal bone, so shock absorption in this area of the hoof is limited and concussion travels up the leg. With a toe first landing the deep digital flexor tendon is under increased tension and squeezes the navicular bone. This eventually leads to damage to the navicular bone and lesions on the tendon.
Below: The deep digital flexor tendon (outlined in purple) passes over the navicular bone (outlined in green).
WHAT CAUSES A POOR DIGITAL CUSHION?
When a foal is born he has digital cusions that are made of soft fatty tissue. This is tough enough to absorb the impact of the foals light weight. As he grows and gets heavier the impact forces increase. Fibrous cartilage begins to grow into the digital cushion and it turns into a fibro-fatty pad capable of absorbing greater impact without the horse experiencing any discomfort. However, for this to happen the horse must be able to move around as it is the pressure and release stimulation and expansion and contraction of the hoof that makes it happen. If a foal has little opertunity to move around or lives on soft ground the digital cushions don't develop properly. Coupled with early shoeing with prevents full expansion/contraction of the hoof the horse can reach adult weight with immature digital cushions. Bar shoes are used in this situation to stabilise the back of the foot and protect the digital cushion. However, the foot becomes weaker, just as the muscles of your arm would if you wore a plaster cast. Bar shoes may keep a horse in work for a few extra years, but don't cause any healing or development of the hoof.
Continued stimulation is necessary to maintain the health of the digital cushion. The following photos are of the same horses feet. On the left she has excellent digital cushions. On the right the digital cushions have weakened and the frogs have receeded. This was due to a year of on and off box rest following a ligament injury. The good news is the digital cushions will build up again once work recommences.