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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TheHorse.com/Step-By-Step 48 TheHorse.com THE HORSE September 2018 STEP BY STEP CHRISTA LESTÉ-LASSERRE, MA I t looks like an ultra-resistant all- weather block, with a shiny, marblelike surface that can trick us into thinking it's indestructible. Its sharply defined edges give us the impression that it's as solid as stone—especially when they land with full force on one of our own feet. And its "clip clop" sound striking against hard surfaces betray it as a dense support structure that works like a steel founda- tion under massive forces. In reality, though, the equine foot isn't like this at all. The foot—or, essentially, the one long toe—is a complex structure filled with bones, tendons, ligaments, arteries, veins, nerves, cartilage, joint fluid, and more. Far from being inert, it's alive and very active, communicating sensory informa- tion, pumping blood, and articulating, contracting, and flexing over ground. And if it's unshod, it's constantly changing shape as the horse uses it, instantaneous- ly as well as over time. The science of the equine foot is like the hoof itself—expanding and contract- ing, getting shaped and trimmed. But as researchers continue to learn more, we can benefit from their knowledge, better understanding how our horses' feet work. And with that knowledge, we can hope to improve the health of not only the feet but also the entire horse. The Evolution of the Hoof The earliest equids, which were the size of foxes, had five-toed feet. They didn't need these toes to grab things, however, benefiting more from better limb swing to run faster. So each middle toe evolved to grow longer and the side toes became shorter. Eventually, the first and fifth toes disappeared, while the second and fourth ones turned into the modern-day splint bones on the sides of each cannon bone. Recently, though, scientists determined that the splint bones are only the top parts of those toes. The bottom parts are still in the foot, says Nikos Solounias, PhD, of the New York Institute of Technology College of Osteopathic Medicine (NYITCOM), in Old Westbury. What we know as the V-shaped frog is actually what's left of the bottom of toes two and four, he says. In his research Solounias followed markers in the embryonic development of the equine foot, which starts out like an unopened tulip with all five toes as its petals. In the adult horse the markers indicate that the top parts of toes one and five appear as bony processes ("wings") coming off the coffin bone. The bot- tom parts of those two toes make up the ridges along the sides of the frog. So in some ways, he's still got five toes in that foot—but four are in "very embry- onic form," says Solounias. "We don't know the role of these rem- nant structures in the real function of the horse," he says. "It could be more for the sensation from the nerves of the five digits and their relation to the brain than actual locomotor mechanics. We're seeing things from a different perspective, and it's important to understand how evolution worked to lead us to the modern horse." A Multipurpose Structure The foot reacts to movement, pressure, and the environment. Unshod, it can react more freely, without the constraints of a rigid interface. "The foot should expand when it receives weight," says Hilary Clayton, BVMS, PhD, MRCVS, Dipl. ACVSMR, McPhail Dressage Chair Emerita at The Facts on Bare Feet ISTOCK.COM What researchers know about the biomechanics of the barefoot hoof Bare feet benefit from plenty of movement over varied terrain and staying free of mud, manure, and urine.

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