To Boot or Not to Boot, is that the Question? | Trainer Magazine | European Trainer Article Index

Jul 1

Jul 1 To Boot or Not to Boot, is that the Question?

AN aversion to using boots in the past few decades probably stems from some research on the temperature of tendons carried out at Bristol University in the early 1990s which showed high temperatures inside tendons of galloping horses. This was followed up by some work by the same group which seemed to show that tendon cells were sensitive to heat and that the temperatures reached during galloping could actually kill tendon cells. But of course boots should be used to offer protection to the lower leg and we know that lower leg injuries are common in racehorses. In this article I will review the issues for and against the use of boots on racehorses. The number one reason for using boots on a horse’s legs must be protection. Boots and exercise bandages are used on horses in the belief that they offer protection against concussion and penetration. In the flat horse the risk of injury comes from brushing (i.e. interference between the two forelegs or two hindlegs) or over-reaching (i.e. a hind shoe hitting the tendon of the forelimb on the same side). In jump horses there is also potential for injury as a result of hitting the fence material. Whilst falls are relatively rare in flat racing, in jump racing falls are not uncommon and there is also potential for injury as a result of crush, concussion, or penetration when horses hit the deck. The lower limbs, and in particular the forelimbs, are the most common site for injury in the horse. In a study of injuries during racing (flat and NH) in the UK over three years, 81% of injuries involved the forelimbs (Williams et al., 2001). One of the things that enable the horse to be so athletic, to move quickly, and to jump so well is its long and slender legs which can move quickly. Most of the muscle is close to the body with the result that the legs can be rapidly accelerated through the air, giving a long stride at canter and gallop. This “streamlining” means that there is little tissue to cushion any impacts on the front of the lower leg, for example from hitting a jump, or from an interference blow from the opposite or a hind leg (brushing, over-reaching). These contacts can damage the bone, joints, and tendons. Damage from concussive blows even where there is no obvious swelling, bruising, abrasion or cut can result in damage to the delicate tissues, including the bone. Think how painful a blow to the front of your own shin is. Whilst many leg injuries may occur due to overuse or overloading, injuries also occur due to trauma to the lower leg that may occur during training and racing. For example, in a study of racehorse injuries in New Zealand by Perkins et al. (2005), one in seven lamenesses were caused by direct trauma (i.e. injury, such as cuts and penetration). At present it is also unclear what role repeated low-grade trauma may have in pre-disposing to injuries such as tendonitis. During exercise the lower limbs of the horse may be at risk from a variety of different traumatic insults. In National Hunt racing, the frontal aspect of the lower fore and hindlimbs may be at risk of trauma from hitting fences. And in both flat and NH racing, horses may be at risk of lower limb trauma due to interference (brushing or over-reaching). The risk of interference is also increased when horses become tired – especially on heavy ground – in hot weather, and/or in the latter stages of a race. The type of trauma may be blunt but there may also be surface bruising or internal damage, abrasion or cutting of the skin, and other soft tissue traumas or penetration. Boots and bandages can potentially offer protection against these types of injury, but there are also potential negatives to wearing boots. Any weight added on to a horse will require an increased effort on the part of the horse to move that weight. This is of course true of a jockey and tack. However, kilo for kilo, weight placed on the limbs will have a greater impact than weight carried in the saddle area. The reason for this is that the limbs are moving faster than the main body. The need to be able to accelerate the limbs quickly explains why they are so light when compared with the rest of the body. Animals with big, heavy legs cannot move them as fast. This is also why there is not much on the lower legs other than bone, some tendons and a small amount of muscle. All unnecessary weight has been “removed”. Any weight added requires more energy to be put in to get the leg moving and more energy to stop it and make it swing back again. Thus, adding small amounts of weight to the end of the leg in the form of a boot increases the effort the horse must put in to run. It is even possible to measure the difference in energy required for a horse wearing ordinary steel shoes and the same horse wearing aluminium racing plates to run (Dr Bob Colborne, University of Bristol, personal communication). In addition, not only can weight increase energy usage but it can also alter the characteristics of the stride. So one important issue in boot design is that although they must offer protection against both blunt trauma (concussive damage) and cutting or penetrative damage, they should also be as light as possible. We should also take into account the potential for boots or bandages to absorb water when in use. Boots that weigh only around 200g each when dry may well be able to hold 100-200ml of water and as 1ml of water weighs 1g, this could double the weight of the boots if the horse was exercising in the rain or on wet grass or if the boots are insulating and sweat produced underneath cannot escape. The next issue relates to restriction of movement. There is widespread belief that boots and bandages can offer support. Whilst there is evidence that athletic taping in human athletes can stabilise joints and potentially reduce the risk of injury, there has been limited investigation of its use in equine sport. If boots are constructed of inflexible (i.e. stiff material) or if boots are applied too tightly, they have the potential to restrict joint movement. Again, there are relatively few scientific studies in this area but Kicker et al. (2004) published a paper in the Equine Veterinary Journal in which they looked at three “support” boots and one “protective” boot. At walk, two of the support boots restricted the range of movement of the fetlock joint, whilst at trot all four boots reduced maximum extension. A recent undergraduate student study at Hartpury College by Jadine Birchall (supervised by Kathryn Nankervis) also seems to support these findings. The average range of movement of the fetlock joint in five horses during walk, trot, and canter exercise was 42° (degrees) without a boot and only 36° with a boot. Tight boots and bandages also have the potential to rub and cause inflammation and injury, especially if applied tightly over the tendons. Another concern with boot and bandage use during exercise relates to heating. Tendons are elastic structures and as they are repeatedly loaded (when the limb is on the ground) and unloaded (when the limb is in the air), they generate heat. Some work by Alan Wilson and Allen Goodship (1994) at the University of Bristol showed that the temperature inside the tendons of horses galloping without boots on could reach 45°C. This was second highest only to muscle temperatures. The tendon temperatures are very high not only because of heat production within the tendons but because tendons have a relatively poor blood supply, which in any other tissue would help remove heat. Are these temperatures of concern? In 1997 the same group of works published the results of a scientific study in which they showed that isolated tendon cells in culture were sensitive to heating. When tendon cells were heated for ten minutes at 45°C, around 10% died, but when they were heated to 48°C then around 80% died. These results were also confirmed by a more recent study of equine tendon cells in Japan (Hosaka et al. 2006). This study also showed that the higher the temperature, the more tendon cells died, and furthermore, it showed that inflammatory mediators were released after heating. Many people have dismissed these studies by stating the view that tendons consist of both cells and non-cellular matrix (the elastic part of the tendon). However, inflammatory mediators are chemicals and hormones within the body that cause inflammation (heat, swelling, pain) and tissue damage. They can damage both the living (cellular) part of the tendon and the non-living mechanical part of the tendon. If tendon core (central) temperatures can reach 45°C during a few minutes galloping without boots, it is almost certain that they will get even hotter when boots are being worn. The veterinary and racing world was not slow to pick up on these studies, and this led many trainers to try to limit the use of boots except in those horses where it was essential to maintain soundness. In the light of these studies, it would seem important to make sure boots are used only during the period of actual exercise and not left on for long periods before or especially after exercise. It would also seem ideal to choose boots that allow heat loss and do not insulate the lower legs, keeping the heat in. Removing boots soon after exercise and cooling the legs would also seem to be advisable. The fact that the lower leg gets hot during exercise and even hotter when boots are used presents another potential problem: sweating. When boots are removed the leg underneath is often very wet from sweat. When skin is in contact with moisture for a long time it becomes hyper-hydrated; this is the effect you see if you stay in the bath for too long. Wet skin cannot “breathe” normally and it becomes more permeable, allowing greater absorption of anything on the skin. Wet skin is also more susceptible to mechanical damage, with an increased risk of abrasions and grazing. Finally, wet skin is more susceptible to bacterial or fungal attack and hence a potentially increased risk of conditions such as mud fever, caused by the bacterium Dermatophilus congolensis. Other potential problems related to comfort can include boots that are too inflexible, boots that slip, boots that allow surface material to become trapped underneath (which may be an important issue on all-weather or dirt tracks), overtight application (which may restrict blood flow and lead to tendonitis), and poor hygiene related to insufficient cleaning of legs and boots (leading to dermatological conditions). Lower limb injuries to racehorses during training and in racing are extremely common and can have career- or life- threatening consequences. A variety of factors have been identified as affecting the risk of limb injury in racehorses including gender, racing history, race interval, race length, going, time in training, number of starts, type of race, age, type of shoe, and degree of fatigue. To date no study has proven whether boots significantly decrease the risk of injury. To a very large extent that will depend on the design and quality of the boot being used. By far the most critical issue in deciding whether to use boots or bandages during training or racing must be whether there is a need for some form of protection that would reduce the risk of either repeated low-grade trauma or severe isolated potentially catastrophic injuries, such as a tendon laceration. Whilst severe traumatic injuries to the lower limbs are easy to identify and explain (e.g. an over- reach), the effect of repeated low-grade blunt trauma with no obvious external damage has not been extensively studied and may contribute to accumulated damage to bone, joints, and tendons over time. Individual horses may also be at greater risk of injury due to other factors such as conformation, previous history of injury, pre-existing injuries, and concurrent injury. The issues to weigh up when considering whether to use boots or bandages include weight, comfort, restriction of movement, and heating. If the decision is still to use any form of leg protection then it is paramount that this must offer sufficient protection in the event of concussive or penetrative trauma to the lower leg area.

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