It’s an iconic sound alright; a metal shod horse travelling on hard ground. Some would say it’s music to a horseman’s ears. But what you’re hearing is high frequency vibration; the tiny portion of vibrating energy that escapes the impact zone and disperses through the air. Most of the vibration, however, travels into the hoof.
So what’s the big deal about a little bit of vibration?
Continual, repeated exposure to vibration is cumulatively damaging to living tissue. It disturbs the circulation of the tiny peripheral blood vessels, affecting the health of bones, connective structures, muscles and even nerves.
The higher the frequency, the more damaging is the vibration.
Metal has a crystalline lattice structure that is rigidly organised and not very elastic, which means that impact applied to one side passes straight through and out the far side as vibration that resonates at a high frequency.
Energy vibrating through horseshoes is amplified by concentration through a small surface area (the hoof wall is only about 10% of the total ground surface area of a hoof).
Combine this with the concussive shockwave being malabsorbed (the equine hoof is designed for concussion to be absorbed mostly through the frog and digital cushion and only minimally through the hoof wall) and add to the equation the weight of rider and saddle and... it just can’t end well.
Fortunately, modern technology is gifting us better options than hard shoes on hard ground.
The Australian summer stills rocks with ground no less hard than it has always been, but in recent years the old familiar clip clop has been somewhat muffled. More and more horses are spending the dry months in soft and flexible shoes made mostly from polyurethane (known as polyshoes).
Why is plastic better than metal on hard ground?
Plastics are viscoelastic which means their internal structure has negligible organisation, long flexible molecules and empty spaces so there is not a direct transfer of energy from one side to the other. Any vibrating energy which enters plastic is effectively dampened down and any vibration that leaves the structure is very low in frequency and amplitude.
Poly shoes are not new
Polyshoes have been around for well over a decade now, but the early models were quite limited in their application and success. They were either too soft to block and hold and therefore secure nails, or they were too hard and became concussive and slippery.
Fortunately, a few years ago the Easycare company (famous for pioneering hoof boots) began to branch out into manufacturing polyurethane horse shoes, mainly for gluing on; a natural progression from their glue on boot bases (called shells) that had revolutionised endurance riding.
One particular model they released is called the Easyshoe N/G which could be either nailed or glued (hence the name N/G). This shoe is predominantly polyurethane but contains a sliver of steel encased within each branch; a soft and fully flexible shoe with just enough steel to hold a nail head so it can be clenched against the hoof wall.
The Easyshoe N/G has been a runaway success story, overcoming the problems that existed with earlier models of nail on polys. They had invented a polyurethane based shoe that was soft enough to dampen impact on hard ground, but would still hold tight clenches right to the end of the shoeing cycle and hooves wearing these shoes would not suffer hoof wall breakdown after subsequent reshoeings.
Please note that the author is not getting any kickbacks from the company that makes these shoes.
Since beginning to use the Easyshoe N/G, the author (who works full time as a farrier) currently has about 200 of his client’s horses wearing them in numerous equestrian disciplines including dressage, eventing, jumping, trail, school, pony club, stock working and camp drafting to name a few.
Polyshoes aren’t perfect yet (what is?), but there seems to be a lot of happy horses and happy jockeys.
The benefits of polyshoes
There is no doubt that horses move better when they are wearing soft shoes that cover most of the ground surface of their hooves. At risk of sounding clichéd, it really does put a spring in their step.
Interestingly, improved movement has also been noticed in horses working on soft dressage arenas. There must be more to this story than just the hard ground.
Accelerated hoof growth
It seems that polyshoes significantly stimulate hoof growth. There is certainly no need to add biotin. A six week shoeing cycle would be the absolute maximum and refitting is usually needed every five weeks. If you think a good shoeing job is one that lasts for six months, then it’s likely that polyshoes are not for you.
Fast hoof growth is good. It grows out the old nail holes before the next shoeing.
There are possibly two factors accelerating hoof growth, both of which are related to the vibration.
When the vibration is dampened as it travels through the viscoelastic structure, it resonates at a significantly low frequency (hit a polyshoe with a hammer and there is a dull thud, not a high pitched ring).
Whilst high frequency vibration is known to be damaging to living cells, low frequency vibration may actually be stimulating and regenerative.
There is also a bit of a misnomer when we say that energy is ‘absorbed’ by a soft plastic structure, because energy is never used up or lost, it is only ever transferred into another form (in this case heat), momentarily stored and then moved somewhere else. Maybe this perpetual warmth also stimulates extra growth.
Better hoof growth
Hooves that are repeatedly shod with polyurethane seem to grow a healthier and thicker sole. Often, this solar growth is white as snow and quite robust, which the author assumes is a sign of optimum health.
Why a thicker sole?
The exact reason behind this phenomenon is unknown, but it could arise from the low frequency vibration that stimulates cellular division, or it could be due to the flexibility, when the shoe expands immediately under load and then springs back when the hoof leaves the ground, thus stimulating the mechanism of the caudal hoof which may add extra material to the solar ‘pool’.
There have been numerous horses that have carried the battle scars of chronic laminitis in the form of unhealthy thin soles and when these horses have then been shod for a while with polys for simple protection in the paddock, not expecting their hooves to ever recover, they have grown sole like healthy horses. This is hard to ignore.
The hoof walls also seem to grow healthier and more supple and old nail holes seem to be more benign than they are when wearing metal shoes. Maybe this is because the shoe flexes more than the hoof wall, so most of the pressure on the nails is transferred to the shoe and away from the wall.
Horses are on their legs most of the day. In fact, apart from some short stints of quality sleep laying down, they mostly sleep standing up. This is only possible because they evolved with a stay apparatus that enables them to lock their legs and remain standing with no muscular effort.
It’s a neat trick, but a horse needs comfort in its caudal hooves because it literally stands down into its frogs to fully engage the stay apparatus.
Polyshoes appear to provide enough 24/7 comfort that horses are able to fully expedite muscle and connective tissue rest. Maybe this relieves local inflammation.
The author works with numerous musculoskeletal therapists who are regularly reporting that horses with niggling soreness, which have been changed to wearing polys on hard ground, have shown considerable improvement. Consensus suggests that it’s due to improved and sustained comfort levels.
Polyshoes are exceptionally easy to use. They mould to the outline of the hoof so no anvil is needed (not that poly can be shape-changed with a hammer – that is unless there is more metal than poly which would defeat the purpose anyway).
Polyurethane is surprisingly tough and resilient. The shoes nearly always go back on for several refits (which makes them quite cost competitive in the long run).
Polyshoes seem more secure than metal shoes and less likely to be pulled off prematurely. If a poly shoe suffers interference, instead of coming off, it usually bends with the insult and then springs back into place.
Multiple attachment options
Polyshoes can be nailed or glued and even potentially screwed on.
Nailing is the author’s first choice because it is practical, cheap, quick and effective. The shoes can be successfully held in place just with slim nails which helps to limit the amount of hoof wall damage.
Gluing certainly has its place, especially with poor quality hooves that won’t hold nails (although the author has found that most poor quality hooves will actually get better after subsequent refits in polys). However, gluing can be expensive and time consuming and success can be fickle and all glues dry quite rigid which negates the flexibility of polyshoes.
Limitations and/or issues arising with polyshoes
Polyshoes are not necessarily suited to all horses in all scenarios.
No one method of hoof protection is flawless and suitable in all situations. If anyone suggests otherwise they are more inexperienced than they realise.
There are still situations when metal shoes may be the only practical and rider safe solution (ie: high level jumping, racing).
In terms of sustainable hoof protection, the author still believes that hoof boots should be the first port of call (if the situation allows) because they are taken off afterwards and the horse gets to live barefoot in the paddock and horse owners have ready access to the hooves for maintenance trimming. This is the regime that grows the best possible hooves.
The grip afforded by a soft edged poly shoe is obviously not as effective as a sharp edged metal shoe. If a horse requires grip to perform under saddle, this limitation can be somewhat overcome because polyshoes can be easily set up to take studs.
Some horses put excessive pressure on the caudal hoof structures and the frog cops the brunt of this. Constant contact with polyurethane may degrade such frogs. If this appears to be the case, the frog support can be removed for a few cycles to let the frogs recover.
Poly shoes certainly don’t glint in the sun like a new set of metal shoes.
Apparently this matters for some horse riders, but the author, being one who is not much bothered by bling, keeps hearing the words of a famous old horseman who often said “pretty is as pretty does”.
For those who do care about the finer points of hoof vogue, it’s a good thing that Hoof Black sticks well to polyurethane.
Polyshoes often don’t look pretty towards the end of a shoeing cycle because they are totally flexible and they allow the hoof to expand in all directions. Basically, as the hoof grows, the shoe expands with it.
From a horse’s viewpoint, untidy but expansive is far better than the polar opposite of hooves encased behind solid metal side-clips, which are neat, yes; but looking at the big picture, the long term picture, such hooves are bound and constricted and a cherry ripe conduit for vibration.
Functionality should be prioritised well above cosmetics.
Polyshoes are not a wet season shoe. They have a greater surface area than metal rim shoes and the ‘porous’ surface becomes a potential bacteria trap. The smell is a bit of a giveaway, although the accelerated growth of healthy tissue seems to outpace any bacterial advance.
There is some scope for removing all frog support and some of the inner edge of the rim when polys are used in wet conditions. This opens up the ground surface of the hoof for greater self-cleaning and also for improved success of topical treatments.
If a hoof is collapsed to the point of being convex instead of concave, a flexible polyshoe may inadvertently exert too much pressure where it touches the sole. Such hooves may be better suited to hoof boots with sculpted pads until concavity has returned.
Polyshoes are still very much first generational and, whilst proving already to be a worthy alternative to metal especially on hard ground, they will only get better and cheaper as market forces continue to strengthen demand.
If you would like to learn more about the primary underlying science that these articles are based on, why not come and hear it from the source - from Prof. Robert Bowker, Head of the Hoof Laboratory Research Team based at Michigan State University in the United States. Prof. Bowker will be conducting a weekend seminar that is open to all comers, including industry professionals and progressive horse owners.
- When: 11th and 12th May 2019
- Where: Dayboro (West Brisbane), Queensland.
- Further details contact: Maja Stoker 0417 325 222
- Click here for more.