Ask the Vet: Podiatry (Shoe Fitting, Balance)

Courtesy of AAEP

Question: I am wondering if there is a special way a horse with a cyst on the flexor surface should be balanced or shod to take away some pressure from the cyst.

Answer: The deep digital flexor tendon exerts a compressive force on the navicular bone. During certain phases of the stride the compressive forces on the navicular bone increase due to the angle of the coffin joint and increased tension in the deep digital flexor tendon. The angle of the coffin joint plays an important role in in the amount of pressure applied to the navicular bone. In both normal horses and horses with navicular bone disease, pressure on the navicular bone increases during the late stance phase of stride just before the heels leave the ground at the beginning of breakover.

In horses with navicular disease, there is a much higher loading rate on the bone during early stance phase (the time in stride when the fetlock starts to rise after reaching maximal extension during the load phase). It has been common practice to shorten “navicular horses” toes in an effort to speed up breakover with the expectation to reduce navicular bone concussive forces.

The length of the toe, length of the heel and the angle of the hoof have an effect on the angle of the coffin joint, which does affect navicular bone compressive forces but now toe length and hoof angle affect pressure on the navicular bone is complicated and sometimes the research is contradictory. Toe length and hoof angle do not affect the duration of stance phase of stride but breakover duration is significantly prolonged in barefooted horses with longer toes. Breakover is not significantly different when rocker-toe, rolled toe or square toe shoes are compared to plain steel shoes.

Some research has reported heel wedges, in the form of wedge pads or wedged shoes, will reduce tension in the deep digital flexor tendon and subsequently reduce compressive forces on the navicular bone. Research with eggbar shoes indicate that force on the navicular bone is unchanged in sound horses but one study reported a significant unloading effect in some horses with navicular disease (type and cause of the navicular disease was not reported). Toe position relative to navicular bone compressive forces has also been evaluated.

Some studies indicate that moving the toe back, either by applying a four point trim or fitting the shoe behind the natural toe, make breakover start earlier and shorten the caudal phase of the stride but result in little or no decrease in navicular bone compressive forces. There has been some anecdotal evidence that “navicular horses” are more comfortable with a reduction in traction qualities of shoes. It is thought by some that shoes with less traction allow the foot to slide more on impact resulting in less “jarring” experienced by the foot.

My recommendation is to work closely with your farrier to find a unique trimming or shoeing that makes your particular horse more comfortable and functional. Use the information presented above as a guideline.

Question: What are the ideal shoes for a barrel horse?

Answer: Selection of shoes for any horse should be based on conformation, hoof health, environment, style of locomotion (travel and action), intended use and expected working surface. Shoes, for performance purposes, are generally applied to horse’s feet when: 1) attrition (wear) is faster than growth, 2) a gait fault can be manipulated, or 3) when more (or less) traction is desired. It is important to remember that application of shoes may alter a horse hoof growth pattern, add weight to the distal limb and alter a horses hoof, limb and locomotion biomechanics. The choice of a shoe for any horse should be customized and made in concert with the owner, farrier and veterinarian using the information listed above. When considering shoes specifically for a barrel horse, consider the individual horses way of “working” the barrel. Some barrel horse hold the ground well and work from the hindquarters while others depend more on their front end and run around the barrel.