The correct amount of traction is crucial to a horse's performance and soundness. Either extreme--too much or too little--significantly changes the way a horse moves and also increases his risk of injury.
Sometimes, low-traction shoes are desirable. Reining horses, for example, wear sliding plates on the hind feet to enable them to make their characteristic sliding stops. For the most part, however, when traveling on slippery footing a horse with inadequate traction is insecure and cautious in his movements, taking shorter steps and crouching to lower his center of gravity and keep his balance. "This puts more stress on his joints," says Goodness. "In contrast, if he has enough grip he won't be so worried about falling and won't be so guarded in his movements." For example, if a dressage horse has adequate traction, "his movements will outshine those of a horse with less traction--just because he trusts his hind end to be more able to carry himself properly," Goodness adds.
But too much traction is also damaging. The equine foot is meant to slip slightly on impact. This more gradual deceleration helps dissipate the forces of the impact and reduces the shock the hoof, bone, ligaments and joints must endure. Racing Thoroughbreds, for example, were found to have a greatly increased risk of catastrophic injury, especially suspensory apparatus failure, if they were shod with toe grabs--ridges on the front of the shoe meant to improve traction.
There are many ways to increase traction on shoes and the key is matching the method with the work the horse does and the conditions he must contend with.
• Calks are protrusions that are as part of the shoe; studs are separate elements that are either screwed in or driven in by the farrier. Both provide traction by sinking into mud, grass or other slick, soft surfaces. "If a traction device must be added you are better off with calks you can screw in when needed and take out for the rest of the time," Nelson says. It's rare that a horse would need the studs for the entire period when the shoes are on, but, she adds, "there are times it's nice to have that extra calk for certain conditions."
The placement of studs and calks on the shoe is determined by the type of traction needed. Applied at the heel, studs and calks provide traction as the hoof lands, to reduce forward slide; these benefit horses such as show jumpers, who may work on wet grass. Those applied near the toe supply traction when the hoof leaves the ground--a benefit to, for example, draft horses pulling heavy loads on pavement.
• Tungsten carbide is a super-hard material contained in several products, such as Borium and Carbraze. Shoes can be purchased with these products preapplied, or a farrier can add them. Because of the higher heat needed to apply the tungsten carbide, the products can be used only with steel shoes.
The rough, hardened material digs into smooth, hard surfaces and give horses added traction on asphalt, concrete and rocky ground. Depending on how much traction the horse needs, the products can be applied as spots at the heels and/or toes, or it be used to spread across the entire surface of the shoe. When built up into studlike projections, Borium can also provide traction on soft surfaces.