Veterinarians: Manage Feet for Function
Because 90% of front-end lameness in horses occurs in the foot, hoof-related issues continue to be a hot topic in veterinary medicine. Duncan Peters, DVM, MS, Dipl. ACVSMR, associate professor of equine lameness and sports medicine at Michigan State’s College of Veterinary Medicine, and Andy Parks, MA, VetMB, MRCVS, professor of large animal medicine at the University of Georgia’s College of Veterinary Medicine, hosted a table topic discussion on foot lameness at the 2014 American Association of Equine Practitioners Convention, held Dec. 6-10 in Salt Lake City, Utah. The room was packed with interested practitioners who offered a variety of suggestions on specific foot issues.

Thin Soles

The first topic on the “table” was thin-soles, particularly in horses that develop chronic abscesses. “Trimming the sole too thin is one of the quickest ways to make a horse go lame,” Parks said. “It isn’t enough to have a thick sole, but the quality of the sole must also be appropriate as must be the integrity of the white line attaching the sole to the wall.”

Attendees agreed that using pea gravel as a paddock base helps improve solar weight-bearing in barefoot horses. Dental impression material (which is commonly used beneath a pad and shoe to provide evenly distributed support for the hoof soles, bars, and frog), on the other hand, might actually inhibit wall/sole growth by applying constant uniform pressure in a shod horse. Many audience members commented about what regulates sole growth. Usually, growth occurs in response to pressure, making it likely that there are mechanoreceptors in the hoof wall. Long toes and low heels are known to be associated with thin soles. Lateral radiographs might reveal a small amount of coffin bone rotation that hinders growth of the solar corium (the soft tissue layer that connects the coffin bone to the rigid hoof capsule and contains the hoof’s blood supply). Wooden shoes seem to work well for unloading the sole where bruising would otherwise cause inflammation and curtail growth. They also facilitate fast breakover to improve a horse’s comfort.

Navicular Disease

Navicular disease is an ever-concerning topic for horse owners and veterinarians alike. The objectives when seeking to relieve heel pain are to unweight the deep digital flexor tendon, ease foot breakover, and distribute the weight to more solid areas of the foot. Farriers should trim horses’ heels and frogs in the same plane so they share the load equally. Shoeing options that help relieve heel soreness include the rock and roll shoe, a Tennessee navicular shoe, a wooden shoe, and an open toe egg-bar.

Keep in mind that these shoes by their very nature change the way the horse weights the foot and moves, which can have unexpected consequences “Often, if we do one thing to fix something, then another area is affected,” Parks noted.

“Deal with the something first, then make adjustments,” Peters added.

Coffin Bone Fractures

Next, the discussion turned to coffin bone fractures. To manage these, many audience members said they like to apply a shoe with a full rim around the entire foot or a fiberglass rim cast (which encases the hoof) with impression material for two months. Most agreed that they’ve found success with conservative management (providing mechanical support rather than surgery), particularly when treating mid-sagittal (through the middle of the bone) fractures. Once again, attendees touted the wooden shoe as useful because its round bottom relieves unilateral foot distortion that could otherwise distract (separate or pull apart) the fracture edges.

Underrun Heels

Veterinarians then moved on to the subject of underrun heels and negative palmar (front limb) or plantar (rear limb) angles (the angle the coffin bone makes with the ground); a negative angle means the back of the coffin bone is lower than the front of the bone, rather than both ends being level. Parks mentioned a study in which researchers determined the two most important variables related to pressure on the navicular bone are a) the coffin bone angle, which can be adversely affected by underrun heels, and b) the ratio of heel to toe height, (i.e. low heels have less height than the toe, which puts more pressure on the heel and the navicular structures).

But before setting out to correct those, keep in mind that “if the horse is performing well, then there may not be any need to modify the foot too much,” Peters said. “There is no point in putting a ‘pretty’ foot on a horse if it is less than functional.”

Crushed heels tend to lead to degeneration of the digital cushion (fibrocartilaginous tissue within the back portion of the internal hoof) and potentially irreversible damage. Underrun or collapsed heels still leave the farrier some heel to work with, but if allowed to persist for too long could lead to an irreversible condition. The frog needs stimulation, which farriers can accomplish by removing shoe bars and/or sole packing material. One participant mentioned that the more underrun the heels in racehorses, the greater the potential for catastrophic fetlock failure.

Coronary Band Circumference

Another note of interest came out of a study from Brazil and Australia showing that coronary band circumference decreases in young horses with race training but increases with rest after coming out of training. Impact and loading can alter the shape and configuration of the hoof over time, while hoof structures can be restored to more normal parameters when given time and rest.

In Conclusion

Parks summed up the current state of managing foot problems: “We think we can fix all things with the foot by putting something on the bottom of the foot,” he said. “Maybe we should also be paying more attention to the muscles and tendons higher in the limb that control the position of the bones of the digits.”