Research paper by University of Utrecht, Netherlands, 2005
The polyurethane horseshoe and its positive effects on joints and ligaments
The results gained in the study carried out at Utrecht University suggest that plastic horseshoes have positive effects on the horse’s locomotor apparatus. Polyurethane horse shoes can be used to great advantage when dealing with pathologic diseases. In the following testing methods and materials will be explained. *

One of the horseshoes tested was the Thoroflex® polyurethane horse shoe produced by the German company CERA, which weighs 166g and has a thickness of 14mm. The flexible horseshoe is made up of polyurethane and its shape is very similar to that of a steel shoe. The basic idea of Thoroflex® is to address the biomechanical needs of the equine foot, i.e. the sole, the outside wall and the frog also accept weight-bearing. *The horse shoe is furnished with three clips in order to reduce the higher transverse force the nails have to withstand, thus preserving the hoof wall and improving the horse shoe’s stability. The other horseshoe tested was a conventional steel shoe produced by Mustad® (weight 475.3 – 520.30, thickness 10mm). Wholesalers offer keg shoes in different sizes and versions.

Tests were also carried out with barefooted horses, with no shoe restricting the horse’s natural movement. The hoof was trimmed like a shod one.

Materials and methods
A certain amount of horses was needed to gain representative results providing scientific data. When planning the study, the participants agreed to test 12 horses. However, it was quite difficult to find horses that met the specified criteria. The most important thing was to find horses with similar kinetics.

Testing methods
After the trimming procedure an aluminum plate was always fixed in the same position on the hoof of the left forefoot. The accelerometer was screwed on the aluminum plate. The accelerometer provided continuous measurements of the acceleration in horizontal (x), vertical (y) and diagonal (z) direction.

Twelve sound horses of different age were successively shod with three types of shoeing (polyurethane shoe, steel shoe, unshod) and tested. Each horse had to provide at least six correct measurements under each shoeing condition.

For each stride selected the maximum amplitude of vertical and horizontal forward/backward acceleration at hoof impact was calculated. Vertical (x) and horizontal (y) acceleration were selected for analysis as they show a very clear picture of damping and sliding properties. The three different horseshoes were statistically compared by means of a variance analysis, with the successive measurements being taken into consideration. “Horseshoe” and “Measurement” were dependent variable.

Table 1 shows the mean maximum deceleration in vertical direction, i.e. vertical landing forces occurring in the hoof capsule at hoof impact. The difference between the three types of shoeing shows that the maximum vertical deceleration measured at the plastic horseshoe is decisively lower compared to the conventional steel shoe or the unshod hoof.

Consequently, the plastic horseshoe tested shows significantly lower results as far as the amplitude of vertical deceleration is concerned than the unshod hoof or the conventional steel shoe.

Table 2 shows the mean maximum deceleration in horizontal direction, i.e. the sliding properties of all three types of horseshoe. The lower the horizontal deceleration is the more the hoof slides on asphalt. The mean maximum horizontal deceleration measured at the Thoroflex® plastic horseshoe is decisively lower compared to conventional horseshoes and unshod hooves. As a result, the use of plastic horseshoes means less horizontal acceleration compared to unshod hooves and conventional steel shoes.

The RMS (Root Mean Square) is calculated in table 3. It is not surprising that the RMS shows the same pattern as vertical and horizontal deceleration. Therefore the RMS calculated for the plastic horse shoe is decisively lower than for conventional steel shoes and unshod hooves. *

Only a few equine research studies used accelerometers to analyze the kinematics of motion. The study carried out in Utrecht proves that the acceleration occurring in the hoof capsule during hoof impact can be measured exactly.

Orthopedic injuries caused by shocks and vibrations at hoof impact could be reduced by riding on track surfaces absorbing these initially high loading forces.

However, the horse has to cope with many different track surfaces, which do not always offer optimum support for the horse’s locomotor apparatus by reducing shock. Therefore it seems to be quite logical to solve this problem by means of the horse shoe. Due to its shock absorbing properties, the ThoroFlex® plastic horseshoe is especially appropriate for hard and stony grounds. The mean value of the maximum deceleration of the plastic horseshoe was 343 m/s?.

According to studies, the hoof capsule of a horse trotting on gravel stone undergoes an acceleration of 372 m/s?. In fact, the ThoroFlex® horseshoe actually reduces the acceleration occurring in the hoof wall during impact. If the horse is shod with ThoroFlex®, it trots as comfortably on hard asphalt as it does on gravel stone with conventional steel shoes.

*It was expected that the results gained in the study will show such massive differences between steel and plastic. We were surprised, however, that the maximum deceleration of the unshod hoof was significantly higher compared to hooves shod with plastic.

Looking at the vertical maximum deceleration shows that the steel horseshoe increases the initially high loading forces, while the plastic horseshoe provides in fact even better shock absorbing properties than the unshod hoof.

There is an even more significant difference between the two types of shoeing as far as deceleration in horizontal direction is concerned (see table 2). The horizontal deceleration describes the sliding properties of the different types of shoeing on asphalt. Sliding properties of unshod hooves and steel shoes are similar (see table 2). Shortly after shoeing the plastic horseshoe slides more than the steel shoe.

It is assumed that this remarkable difference derives from a thin plastic layer, which results from the manufacturing process of plastic. However, this layer is worn down after a short period of time. As nails protrude shortly after shoeing when steel shoes are used, loading is not balanced-out and consequently the hoof slides only little. Especially in this sector further investigations would be necessary to prove or refute this theory.** *

The RMS is the root mean square of x, y and z acceleration. All this data show that horses shod with ThoroFlex® experience lower deceleration in vertical and horizontal direction.

Comparing the results gained in the study to human sports shoes, which are all biomechanically tested, suggests that orthopedic injuries could be minimized by using a light-weight, flexible and shock-absorbing plastic horseshoe. Furthermore, joint diseases or injuries caused by wasting could be reduced or even avoided.

Therefore especially endurance horses and carriage horses benefit from plastic horseshoes as they mainly trot on asphalt. It is also beneficial to horses already suffering from arthritis and other joint diseases. Horses that mainly trot on smooth surfaces can hardly gain from the shock-absorbing properties of plastic horseshoes. However, they also benefit from the light weight of the horseshoe.

The study carried out in Utrecht proves that the plastic horseshoe tested reduces shocks and vibrations, thus keeping the horse’s locomotor apparatus sound and guaranteeing a long, healthy live.