- Dec 1, 2001
Tough. Resilient. Protective. Whether on a human foot or a horse's hoof, a shoe supports weight and helps one overcome environmental hazards. With today’s technology, equine footwear can "stick" to a hoof without the traditional nails. Tough synthetics allow a shoe to adhere to the bottom of the hoof, or fit around the hoof wall. A shoe doesn’t even have to exist as a pre-formed shape -- a talented farrier can sculpt a customized form to address your horse’s unique hoof problems.
Adhesive substitutes for metal shoes have generated a specialty area of hoof care. Ongoing research has utilized new technology to deliver nail-free materials and methods.
Helping the Hoof
Veterinarians and farriers are always looking for ways to help hooves bear weight. Healthy hooves should breathe, flex to allow normal foot movement, and support the horse’s weight in any environment. In some cases, glue-on shoes help the hoof do these things better than a traditional shoe.
The glue-on shoe has many applications, and more are being discovered. Glue-on shoes can help maintain a hoof’s natural function of support and flexion as they attach through bonding rather than rigid metal being nailed to the foot. For horses with a quarter crack, low-grade laminitis, or weak horn capsule, a bonded shoe can make a significant contribution to the overall treatment regime. For any function that a nailed-on shoe can perform, a glue-on shoe has been developed. For example, a young horse that needs support to correct a limb deviation might wear a glue-on cuff with a toe, side, or heel extension.
Ric Redden, DVM, specializes in hoof care at his International Equine Podiatry Center in Versailles, Ky. He says, "The iron shoe seemed to be a panacea in the days of the Romans. But there are drawbacks in the iron shoe with nails."
Some hooves can’t tolerate nails. Nails can split a weakened hoof wall, forcing farriers to seek a deeper and higher location for attachment. Unfortunately, this increases the risk of injuring a horse (hot nails) or creating an uncomfortable, tight feeling (nail bound) as the nail must lay very close to sensitive structures. It also should be remembered that nails create holes in the hoof wall. That means even the soundest foot must grow new horn to supply solid hoof wall for the next nailing.
Equine professionals who use glue-on products mainly choose them as therapy to treat hoof or lameness problems. Used with a hoof repair compound, a farrier can rebuild a damaged hoof and affix a shoe with little trauma to the existing hoof wall.
"The glue-on technology has been great," says Redden. "If you have a hoof that’s marginal (too thin or broken) to put nails in, it’s quite easy to attach a glue-on shoe to serve the purpose. You can do it several times in a row and have tremendous results."
Rob Sigafoos, a Certified Journeyman Farrier who invented the Sigafoos Series One and Two shoe, works in the Applied Polymer Research Laboratory at the University of Pennsylvania’s New Bolton Center. He has taken the use of glue-on shoes to the next level, using them in everyday work.
"Less than 1% of the horses we shoe are shod with nails and shoes," says Sigafoos. "Eighty percent are shod therapeutically (with glue-on shoes)."
His thought is that an adhesive shoe can help the hoof by preventing problems. He says glue-on shoes help by avoiding nails and allowing the use of more material than a farrier could use with a traditional shoe.
He also says that glue-on shoes can function as a permanent shoe replacement for enhanced performance. "Twenty percent of the horses we shoe (mainly competition horses) are shod prophylactically (preventively) for people who can’t take a chance of that horse getting a bad nail," he adds. "Those people opt for the glue-on shoe."
He notes that individual horses inspired their glue-on products. The Applied Polymer Research Lab is constantly looking for new ways to treat various hoof and lameness problems. New products are patented by the lab and licensed to outside vendors.
"Necessity is the mother of invention," says Sigafoos. "We have a tremendous case load at New Bolton Center. The kinds of problems we see are what other people couldn’t resolve. Many times you are faced with a problem you haven’t seen before, or a problem that isn’t being resolved with current technology."
He adds that testing on products is also done in the laboratory. "We do have a group of horses for in vivo (in the living horse) testing, but most all the work in my lab is in vitro (in the laboratory)."
Materials and Methods
Equine podiatry is taking advantage of other industries’ innovations. For example, synthetic compounds -- mainly polymers -- are commonly used in human medicine and dentistry as well as in protective and leisure activities (from the material of bullet-proof vests to fingernail extensions). The common polymers of acrylic, polyurethane, and polyethylene are used for everything from hip and tooth replacement to the wheels of skateboards. These plastic compounds are durable and resilient, and as bonding agents they can affix a metal shoe or become a supportive, shock-absorbent, lightweight cushion to protect a horse’s foot.
Acrylic is a man-made resin often used as methyl methacrylate (MMA). It’s created by blending a liquid and a powder to form an adhesive that hardens as it bonds. Many companies make various types of acrylics and shoes for horses, and hoof care professionals have found uses for the many types of bonding agents and foot products.
Haffner International Marketing Group Inc. developed Hoof-it, made of cold polymerizing powder and MMA liquid. Owner Heinz Haffner says, "We can make the acrylic very soft, just like the sole, to substitute for a pad. We can vary that (hardness) using more liquid than acrylic powder, so it stays flexible with the warmth of the hoof."
Vettec (the maker of Equi-Thane) uses polyurethane, which is known as a durable plastic, in its products. "The material takes over the wear and tear of the hoof and is still flexible and hard," says Frank Rovelli of Vettec. "A lot of people like urethane because it maintains flexibility when it gets hard. Your foot is always moving. If an adhesive constricts movement, the shoe doesn’t stay on as long."
The Mustad company created the durable polyurethane Glu-Strider shoes, which have pre-formed tabs used to glue the shoe onto the foot. A California farrier with nearly 30 years of experience, Dan Bradley has extensive experience using the Glu-Strider. Of the Glu-Strider, he says, "You can shape the shoe to the foot. Starting at the back, you use a couple of drops of Super Glue, and roll the tab up as you glue. It seals in five to 10 seconds. Go from the back tabs and work your way forward. Then let the horse stand -- the longer the better."
Some shoes -- including the Dalric and Sigafoos -- are attached to a hoof cuff that goes around the wall. The Dalric shoe is an injection-molded, felt-lined urethane shoe with an optional plastic extension that molds around the foot; any shoe can be attached to the hoof using this cuff. Redden, who developed the Dalric cuff with Helmut Dallmer of Germany, says, "I developed this cuff so you can nail or rivet a shoe on it, then attach the cuff to the hoof. It’s used to attach my Modified Ultimates to a foot suffering from acute laminitis, either with a bandage or glue when more permanent attachment is required. This package offers tremendous mechanical advantage in the early stage of the syndrome as it significantly reduces stress on the laminae, often preventing coffin bone displacement."
Other Dalric models are for foals under 12 weeks old. They’re used to support the foot and correct toe-in or toe-out conformation, club feet, or weak flexor tendons.
If an aluminum shoe needs to be attached to the foot, the Sigafoos Series I shoe design allows bonding agents to be used -- an engineered fabric is used to glue the shoe onto the foot. "We use Spectra, an ultra-high molecular weight polyethylene for its strength and abrasion resistance, and the polyester provides the bonding surface," says Sigafoos. "We use a braided fabric rather than woven, so it gives more strength to the hoof wall."
Ready, Set, Glue
In general, a glue-on shoe is applied in a manner similar to putting on a human fingernail extension. The farrier smooths the surface of the hoof wall with sandpaper and cleans it with alcohol. The hoof must be perfectly clean and dry so the bonding agent can adhere to its surface.
The bonding agent must be mixed according to the manufacturer’s directions, and applied as instructed. Some types need to be heated, especially in cold weather, so they can bond the shoe onto the hoof. With some bonding agents, the hoof must be held off the ground until the compound sets and cures (becomes hard).
For the creative farrier, new materials allow free-form building of shoes. The material is applied to the foot in a paste-type state, allowed to harden, and then rasped down just like a hoof wall.
Rovelli describes the process: "You pick up the foot and dispense a bead of material in the area where the shoe would be. Make it one and a half times as thick as the shoe, and the same width as a shoe. Then rasp it down when it sets."
A glued-on shoe can be removed by rasping or clipped off with hoof nippers. Also, acetone can soften hardened acrylic.
Although glue-on acrylic shoes have been around for 20 years, acceptance of glue-on shoes in practice is mixed. Bradley describes his use as "starting at 5%, and now up to 20-25%. We use the glue-on shoes especially on rehab horses."
Haffner says there is resistance from some farriers to glueing on shoes. "We have a composite shoe that the professional can nail on -- some don’t want to glue, so we give them an option," he comments.
The major issues are shoeing time, added expense, and the effects on the hoof. The bonding process does take extra time, sometimes as long as 15 minutes for the material to set. During the first part of this period, the farrier must hold the foot off the ground while the bonding agent solidifies. Adding preparation time, Bradley estimates 45 minutes for the best-case scenario of two shoes; in the worst case, four shoes could take up to three hours.
The cost of glue-on composite (polymer) shoes can be substantially higher than traditional shoes -- a single front shoe could cost a farrier $28, compared with metal shoes that might only cost $2-$3 each. However, they can be reset like metal shoes.
The latest innovations shorten setting time. Of Vettec’s Equi-Thane Super Fast Rovelli says, "It sets in 30 seconds. We found that people make shoes with it because the glue and the shoe are all in one. That allows for a lot of flexibility."
Haffner describes a light-curing dental acrylic that can also be used. "It is a very friendly polymer that is cured with light. It is very fast (to apply) and very durable."
Safety of products has been an issue for humans and the horse’s hoof. A material might have a strong odor and require good ventilation during use, and some bonding agents must be used with gloves. One acrylic, MMA, has been linked with adverse reactions to human nail extensions. Yet, Sigafoos says that they have not seen any adverse effects on horses’ hooves.
"The vapors released by curing polymers are less hazardous, but dust could be a serious health risk," warns Bradley. "When you grind a pad, plastic shoes, or hoof repair material, the dust that comes off it can cause permanent lung damage. You should wear a respirator."
Redden cautions, "Anything you glue to the exterior of the (hoof) horn has a deteriorating problem associated with it. Adhesives collect moisture, and (excessive) moisture is the killer of the hoof capsule. There also is a softening and weakening effect since you are reducing the stress the hoof needs to stay healthy. The more demand a hoof receives, the tougher the hoof gets. The wild horse is a great example (of tough feet), where the hoof is under constant demand. Penetrating or covering it up has an inherent risk of weakening the horn we wish to protect. But often the advantages outweigh the disadvantages.
"It’s a slow deterioration process you have to learn to live with (when using acrylics and glue-on shoes)," adds Redden. "We have not found a way to alter that. It’s one of the drawbacks." However, the deterioration is slow and can be minimized by encouraging a drier environment. Keeping the horse in a dry stall, preferably with shavings, for a few hours daily can help reduce the water content of the horn.
The products themselves are durable, however, lasting four weeks or more. "The wear is fairly comparable to a normal shoe," says Rovelli about Equi-Thane Super Fast. "It will wear quicker than steel and the glue-on shoe made of urethane. The good news is that it gives you the option of creating something custom every time."
Bradley says, "Composite shoes are a temporary solution at present. A lot of broodmares have composite shoes and farriers can keep resetting them (because of minimum wear on the shoe due to the mare’s inactivity and environment). With other horses, you use one shoe maybe three times, then go back to barefoot or the horse’s normal shoeing."
Yet, glue-on shoes continue to gain popularity as they help horses continue their normal activities even when their hooves aren’t totally healthy. As new technologies emerge, proponents expect more successes and increased use of nail-free footwear.
About the Author
Award-winning writer Charlene Strickland lives in Bosque Farms, N.M. She has published 8 books and over 600 magazine articles, and is a member of the International Alliance of Equestrian Journalists.
POLL: University Equine Hospitals