Hoof - Surface Interaction Study

In racehorses, the identification of risk factors for lameness has driven research efforts into lameness prevention strategies. The foot-surface interaction is of particular interest and has been the subject of a lot of research. To date this has primarily been through the investigation of ground-surface composition and properties, in addition to the effects specific surfaces have on the horse’s way of going. Changes in speed, stride length, and frequency have been observed, and the vibrations (shock waves) resulting from the initial foot-surface collision have been measured on different surfaces. However, the surface represents only half the story: what about the foot? In practice it is the foot that we are more likely to influence on an individual level. As part of my PhD studies at the Royal Veterinary College (RVC), we have investigated whether it is beneficial to use novel farriery techniques such as ‘sole-packing’ and padding materials to improve shock absorption in horses exercising upon both firm and soft surfaces. This work has been kindly funded by the Horse Betting Levy Board (HBLB) and the RVC Paul Mellon Trust. Here we will discuss the intricacies of the foot-surface interaction, what is already known about the effect of surface, and how our research into the use of sole-packing materials might be another arrow to our bow in the prevention of lameness in racehorses. What is the foot-surface interaction? The contact between the foot and the surface is over in a flash in the galloping racehorse (or even one trotting slowly, for that matter). However, foot contact may be broken up into four key stages to help us understand and describe the effects different surfaces and farriery techniques have. Stage 1 – Primary impact. The foot has just hit the ground, is sliding forwards along the surface and decelerating. Vibrations are at their largest and fastest at this stage but the force the leg experiences is low because it is not yet supporting the horse’s bodyweight. Stage 2 – Secondary impact. The leg starts to take on the load of the horse’s bodyweight and the force exerted upon the leg starts to increase. Stage 3 – Support phase. When maximal force is exerted upon the leg. Stage 4 – Breakover, or foot off. The heel lifts off the ground, the foot rolls upwards and forwards around the toe (which rotates downwards and into a soft surface) before the foot is lifted off the ground completely. Rapid deceleration and the subsequent distal limb vibrations and high forces are thought to contribute to injuries. It is therefore Stages 1 and 3 that are often considered during foot-surface interaction investigations. The aim of my PhD is to investigate the effects of sole-packing materials upon impact vibrations in horses and therefore this article will mainly focus on Stage 1, primary impact. The surface story so far Whilst musculoskeletal disorders in horses are a multifactorial phenomenon, studies have shown that certain surfaces and surface properties are associated with higher injury rates. Injuries are more likely when the going is firm, and generally dirt surfaces have higher injury rates during both racing and training, where they may increase the incidence of ‘bucked shins.’ Additionally, there is evidence to suggest submaximal exercise (walking) on a concrete surface compared to a dirt surface increases the likelihood of joint pathology developing. In general, as surface firmness increases, the size (magnitude) and speed (frequency) of the vibrations experienced during primary impact (Stage 1) increase too. Absorbing these impact vibrations through the use of specific surfaces and shoeing materials may play a role in reducing the risk of lameness developing. Surfaces have primarily been the target for enhancing shock absorption and there are various ways to analyse them. These analyses help us understand how current surfaces are performing, what affects their shock absorbing capacity, and how we might design the surfaces of the future. Various training and racing surfaces are available at racecourse and training centres around the world. In thoroughbred racing, dirt, synthetic, and turf surfaces have received the most attention from researchers. There are two main approaches to investigating surfaces: Using devices to measure specific surface properties Measuring live horses directly There are multiple devices that have been designed to test racing surfaces. The ‘going stick’ is probably the most well known and is in regular use at UK racecourses. It is used for turf surfaces and measures the force needed to push it into the ground and pull it back out again. This device is particularly useful for monitoring surface properties of individual racecourses over time and is essential for compiling race day ‘going’ reports. The Orono Biomechanical Surface Tester (OBST) is another device. It aims to mimic the foot-surface impact (Stage 1 of foot-surface contact) and the subsequent loading of the limb (Stages 2 and 3). It does this by replicating the speed and load of the leading forelimb in a galloping thoroughbred. The OBST can measure peak load (force) and has the useful ability to take into account the forward sliding of the foot, which sets it apart from other, simpler designs. There are other devices available but these remain the most specific and widely used. Both are particularly useful for ongoing monitoring and investigating the effect of surface management regimes and weather conditions on surface properties. However, they do not necessarily measure the effect upon the moving horse. There are a variety of methods that can be used to measure the horse in motion. These include: force plates, pressure mats, force measuring horseshoes, limb-mounted accelerometers, body mounted sensors, and high-speed video equipment. Some methods are fairly easy to transport to training stables and can be used ‘in the field,’ while others such as force plates can be more challenging. The use of sensors that can be attached to the horse itself and high-speed video cameras have therefore proved highly valuable in horse-surface investigations. A combination of force measuring horseshoes, limb mounted accelerometers, and high-speed video has proved a successful technique for investigating the effect of surface upon harnessed trotters, and studies in other groups of horses have used accelerometers with great success, too. What many surface studies show is that hoof impact vibration increases with surface firmness. However, surface firmness is only one of many properties which must be taken into account when considering surface design. Furthermore, surface properties are also influenced by the weather – particularly rain, which alters the water content, and temperature, which affects waxed surfaces. Designing the ‘best’ surface is therefore a complex task and it is clear that we do not yet have all the information required to achieve this. However, we are constantly moving in the right direction. More information can be found in the ‘Racing Surfaces’ white paper http://www.grayson-jockeyclub.org/resources/White_Paper_final.pdf and the ‘Equine Surfaces White Paper’ http://inside.fei.org/system/files/Equine%20Surfaces%20White%20Paper.pdf So, what about the foot? Despite the regularity with which horses receive farriery attention, there is limited scientific evidence regarding the effect of shoeing. Shoeing is clearly a very practical and successful intervention; otherwise, I’m sure we would not still be doing it after all these years! However, a greater knowledge of the effect of shoeing and shoeing modifications may contribute to the marginal gains that take a horse from second to first. In previous studies, there has been some work carried out on the effect of different shoe materials and shapes as well as foot slip and grip, breakover, and sole-packing and padding methods. With regards to improving shock absorption, the use of plastic shoes and certain packing and padding methods have been shown to reduce the size and speed of the impact vibrations. However, these interventions are not always practical, as non-metal shoes wear out more quickly, and adding materials between the shoe and hoof can cause the shoe to become loose. We have been investigating the effect of pour-in sole-packing materials on hoof vibration in horses. Our studies have explored their shock absorbing ability when used with both steel and aluminium shoes on firm and soft surfaces. We hypothesise that using a pour-in sole-packing material will improve shock absorption and reduce hoof impact vibration size and speed. How have we done this? Our work relies on hoof-mounted accelerometers which measure the impact vibrations (Figure 2). The studies have used both cadaver legs and live horses. The cadaver studies utilised a custom designed device, essentially a slide, which delivers a horse forelimb (sectioned at the elbow) to the ground, simulating the primary impact (Stage 1) in a trotting horse. Aluminium and steel shoes both with and without packing material in place were tested using this method. The limbs were dropped onto both firm (bitumen) and soft (plain sand, and a waxed sand and rubber mix) surfaces. We then performed a very similar study in live horses. An accelerometer was attached to the dorsal hoof wall of the front feet using hoof glue (Figure 3). The accelerometer connects via a wire to a data logger, which records the accelerometer signal. The data logger is mounted on a surcingle while the wire is held close to the leg with a lower limb boot and an upper limb strap or vet wrap (Figure 4). So far, the horses have tolerated this surprisingly well, with only one cheeky pony taking offence! It is in the live horse studies that the benefits of using accelerometers are really seen. They are small and relatively easily attached, so we can take them to the horses in the field to test different surfaces and shoeing materials. This makes it far easier for us to recruit horses into our studies and enables us to collect data from different locations. In addition to the hoof-mounted accelerometers, the horses were also equipped with inertial sensors, similar to those used in studies undertaken at the Singapore Turf Club that were presented in the January issue of European Trainer. The five sensors (attached to poll, withers, pelvis, and both hip bones with double-sided tape) use a combination of magnetometers, gyroscopes, and miniature accelerometers to track movement. The movement of the left and the right of the horse can then be compared to determine if any asymmetries are present. We used these to determine if there were any differences in movement symmetry present between the different shoeing and surface combinations. Once the horses were all kitted up they were walked and trotted in hand, on both a firm gravel surface and a waxed sand and rubber surface, under four different shoeing conditions: steel shoe, steel shoe and packer, aluminium shoe, and aluminium shoe and packer. Getting through all the shoeing conditions in a group of five horses was a bit of a tall order and we are very grateful to our farrier Mark Aikens and his clients who were the guinea pigs in this study! Whilst our data analysis is ongoing we are confident that there are some interesting results to be found. Importantly we have demonstrated that we have a successful and practical setup for collecting high-quality live horse data. It is hoped that we will be able to extend our study into horses travelling at faster speeds. Understanding more about the foot-surface interaction and how it is affected by shoeing and surface will support trainers in making the best training and management choices for their horses. Whilst pour-in sole-packing materials should not be thought of as a miracle cure, they may provide opportunities for preventing and managing lameness with the potential to keep horses in training and give them the best chance of being successful whilst minimising the risk of injury.

By Amy Barstow BVetMed, MRCVS, PhD Candidate

First published in European Trainer issue 58 - July - September 2017

In racehorses, the identification of risk factors for lameness has driven research efforts into lameness prevention strategies.

The foot-surface interaction is of particular interest and has been the subject of a lot of research. To date this has primarily been through the investigation of ground-surface composition and properties, in addition to the effects specific surfaces have on the horse’s way of going. Changes in speed, stride length, and frequency have been observed, and the vibrations (shock waves) resulting from the initial foot-surface collision have been measured on different surfaces. However, the surface represents only half the story: what about the foot? In practice it is the foot that we are more likely to influence on an individual level.

As part of my PhD studies at the Royal Veterinary College (RVC), we have investigated whether it is beneficial to use novel farriery techniques such as ‘sole-packing’ and padding materials to improve shock absorption in horses exercising upon both firm and soft surfaces. This work has been kindly funded by the Horse Betting Levy Board (HBLB) and the RVC Paul Mellon Trust. Here we will discuss the intricacies of the foot-surface interaction, what is already known about the effect of surface, and how our research into the use of sole-packing materials might be another arrow to our bow in the prevention of lameness in racehorses.

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