The Horse

SEP 2018

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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Page 49 of 59

50 THE HORSE September 2018 Michigan State University (MSU) and president of Sport Horse Science, in Mason, Michigan. "Its structures help absorb the shock from the force when the foot comes down on the ground." If the foot is bare (and trimmed cor- rectly), forces spread across the bottom of it—throughout the sole, wall, frog, digital cushion, heels. All these more-or- less-elastic tissues receive diffused im- pact, while structures higher up the leg, such as the pastern, fetlock, knee, and hock, don't experience as much of it. Meanwhile, each footstep plays a vital role in healthy circulation, says Stephen O'Grady, DVM, of Virginia Therapeutic Farriery, in Keswick. "The blood vessels in the equine foot have no valves," he says. "Arterial blood comes into the foot when the horse lifts up his foot, the vessels fill with blood, and it gets utilized. So, when he puts weight on the foot, thousands of capillaries across the entire solar surface of the foot get compressed, pushing blood back toward the heart." Work by Clayton's colleague Robert Bowker, VMD, PhD, professor and head of MSU's Equine Foot Laboratory, indi- cates that heels also have critical sensors for proprioception—the sense that tells horses where they're putting their feet. "They might not feel as well as we do, but it's significant that the proprioceptors are in the soft horn of the heel where the wall is able to move the most," Clayton says. The healthy bare foot usually has thicker soft tissue structures on its bottom surface, including the digital cushions. And that could possibly have protective qualities, says Debra Taylor, DVM, MS, Dipl. ACVIM, associate profes- sor and equine podiatry veterinarian at Auburn University's College of Veterinary Medicine, in Alabama. "When the digital cushion is skinny and long (which is more common in shod horses, she notes), it only supports the center of the navicu- lar bone," she says. "The edges won't have any soft tissue under them; there's just the deep digital flexor tendon (DDFT) directly. So it's only intuitive that if the digital cushion is wide enough, it would have some sort of protective role." How the bare foot functions from a scientific standpoint is not necessarily what happens when shoes are added, our sources say. Shoes can constrict move- ment and restrict expansion by forcing the hoof into a certain shape. And they prevent the bottom of the foot from coming into full contact with the ground. They say the resulting lack of stimula- tion from the ground tends to make the soft structures recede, contract, become softer, and, in some ways, atrophy. What Should a Bare Foot Look Like? Despite having this basic biomechani- cal knowledge, scientists still don't clearly understand how a domesticated horse's bare foot should appear, says Taylor. "It's the only tissue on the horse where vet- erinarians can't agree on what's normal," she says. Research is lacking significantly, she says. In fact, scientists continue to debate the existence of some anatomi- cal structures. "There's a ligament that other scientists have started recognizing recently, under the DDFT on top of the digital cushion, and it's not even labeled in specialized anatomy books anymore," she says. The late Prof. August Schum- mer, PhD, former head of the Veterinary Anatomy Department at Justus Liebig- Universitat, in Giessen, Germany, had described and labeled the ligament in the 1940s, but the structure later disappeared from literature, says Taylor. One thing scientists seem to agree on, however, is that the wild or feral horse foot is not a reliable standard for the domesticated horse foot. "Mustangs and brumbies are not a good model," Clayton says. "They do a different kind of work." Wild horses never have to carry riders, STEP BY STEP COURTESY DR. NIKOS SOLOUNIAS/ROYAL SOCIETY OPEN SCIENCE A B As the horse's foot evolved, the middle toe grew longer and the side toes shorter. Eventually, the second and fourth toes (green and yellow) turned into the splint bones and frog. Toes one and five (blue and red) became the bony processes coming off the coffin bone and the ridges along the sides of the frog. Dandy Products, Inc. Padding & Flooring Specialists "Padding At Its Best" Breeding Sheds, Stocks, Stalls, Trailers, Exercise & Training Areas, Induction & Recovery Rooms Table & Surgical Pads, Neo-Natal Foal Beds Non-Slip Safety Floors for All Areas Pavesafe Bricks & Tiles, Trac-Roll & Vet-Trac Floors, Wash Stall,Grooming, Aisleway and Trailer Mats Toll-Free 888.883.8386 • 513.625.3000 FAX 513.625.2600 3314 State Route 131, Goshen, Ohio 45122 •

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