Plastic Shoes. Latest Developments

Andrew M McDiarmid BVM&S Cert ES(orth) MRCVS
Clyde Veterinary Group
Lanark
01555 66000

Throughout history there have been many attempts to replace steel as the material of choice to shoe horse’s feet.  Leather, rubber and wood have all been tried; in fact used car tyres are still used in Morocco today, much to the detriment of the horse.  Since the 1980s several farriery supply companies have manufactured plastic shoes.  They have come in variety of forms; early versions required the farrier to cut to size the ‘base’ of the shoe with a jigsaw and then apply plastic tabs to the shoe for later attaching onto the hoof wall: others come pre-prepared with numerous extensions that the farrier removed if not required:  some have metal encased in the plastic to provide extra strength; and there are plastic shoes through which a farrier can nail in a traditional way.

Whilst horses continue to be shod with plastic shoes, they are only really used in selected conditions.  The main problem with plastic shoes is that the adhesives used to attach the shoe to the hoof are not strong enough to keep the shoe in place for long periods of time, the shoe doesn’t fit the hoof properly, the plastic can be slippy and many wear through with normal everyday use.   

Approximately five years ago Wiltshire based farrier Andrew Poynton designed a new system that he claims overcomes many of the difficulties encountered with previous glue-on shoes. Andrew, an examiner for the Worshipful Company of Farriers, explains that in designing the Imprint™ Hoof Care System he “wanted to minimise trauma, have a perfect fit, and maximise support without compromising the natural functions of the foot. The shoe had to stay on the foot for the duration of the treatment, and had to produce a result!"

The revolutionary properties of the Imprint™ shoes are due to the thermoplastic used to create them. The plastic becomes pliable at 60ºC and solidifies at 35ºC. It is easily warmed up in hot water, and can then be moulded to the exact requirements. The material is lightweight (the foal shoe weighs 35 grams) and hard wearing, the latest version contains graphite. Water and surgical spirit also do not adversely affect the methyl-methacrylate adhesive.

The shoe is based on a heart-bar design. Its W-flexing bar over the heels and frog allows the shoe to be bonded to the entire lower margin of the hoof wall without preventing expansion and contraction of the hoof. A flange which will contact the hoof wall extends forwards from just in front of the heels. When applying the shoe the foot is trimmed according to usual farriery practice and the bottom border of the wall is rounded off as for a grass trim. The surface layer of the hoof (or periople) is rasped off to provide a smooth clean surface to bond to the shoe. Using a rotary burr, or loop knife, three or four small oval indents are cut in the lower hoof wall before the hoof is cleaned with surgical spirit. The shoe is placed in boiling water and as it warms up it begins to turn transparent indicating it is soft and pliable. When the flange is completely clear, the shoe is removed from the hot water. Adhesive is applied to the inside surface of the shoe. As the shoe is soft when applied it is gently pressed to conform to the shape of the foot. The flange is pressed onto the wall, ensuring that plastic is pushed into all the indents. The adhesive takes 3-5 minutes to set.

The plastic material used to make the shoes is now available as granules, which means that additions to the shoe in the form of extensions can be added to the hot shoe. The Imprint™ granules can also be used for repairing hoof cracks.
By far the most common indication for the use of plastic shoes is in the treatment of horses and ponies with laminitis. Plastic shoes can in general be applied at any stage of the disease because applying the shoes does not create any discomfort for the horse, there is no nailing and the shoe probably has some anti-concussive properties.  Frog support is important for the treatment of laminitis and with all types of plastic shoes it is relatively easy to incorporate this into the shoe. 
The other main application for plastic shoes is in the treatment of limb deformities in foals, predominantly angular and flexural limb deformities.  If these conditions (for example, toed-in toed-out, tendon laxity, carpal valgus, fetlock varus, contracted tendons) are recognised early enough in the foals life they can be reasonably easily treated. Treatment may on occasion require surgery however the average case can be successfully treated with conservative management, usually including the use of plastic shoes.  The benefit of plastic shoes in foals is that the hoof is too small to be shod in the normal way with nails and the flexible nature of plastic means that there is generally no danger of compression on the hoof capsule.

Although these latest developments have brought plastic shoes a lot further than previously there is still considerable way to go before they will replace steel.  Whether we will ever be able to shoe a horse with plastic that will allow you to ride over a ploughed field one day and the next trot for 4 miles on a road remains a long way off !