A riding surface impacts the entire equine musculoskeletal system.
In Joe Johnston's Hollywood depiction of Hildalgo, Viggo Mortenson as Frank Hopkins stoops down to scrape up some of the sand covering the arid Saudi Arabian ground where his colorful mustang will race. His expression is grim, his mouth in a frown as he studies this "track." It's clear he knows the surface is far from ideal for racing, even for hardy mustang hooves.
A less-than-ideal riding surface is an understandable concern. Tragic racehorse accidents frequently call the surface they run on into question (For instance, who could forget Eight Belles' heartrending pair of broken fetlock joints after coming in second at the 2008 Kentucky Derby, or Rewilding's cannon bone break mid-race at Britain's 2011 King George VI & Queen Elizabeth Stakes). Upper level sport horses, like the 2010 World Equestrian Games (WEG) triple-gold dressage champion Totilas or the 2006 WEG individual eventing champion Toytown, sustain lameness-causing leg injuries and have to withdraw from major competitions. Amateur competition mounts and pleasure horses might be retired early due to conditions such as navicular disease. And these scenarios call us to consider: Was it because of the ground they trotted on?
Questions like this lead researchers to study "footing," which refers to the surface horses are ridden or worked on in arenas and fields and on tracks and roads. The field of footing science involves understanding how different kinds of footing affect equine health.
Footing's Full-Body Impact
Despite its name, footing's influence isn't limited to the horse's feet. The interactions between the horse's feet and the footing create various forces that can affect the entire musculoskeletal system, including bones, muscles, joints, tendons, and cartilage.
Footing type (all-weather, natural terrain, traditional dirt/sand, etc.) is unquestionably a potential risk factor in the development of musculoskeletal ¬disorders--most commonly tendinitis and fractures (especially in racehorses), says Nathalie Crevier-Denoix, DVM, PhD. Crevier-Denoix is head of the equine biomechanics and musculoskeletal pathology unit of the Veterinary School of Maisons-Alfort, France, and the French national agronomic research institution. Footing also affects racehorse and sport horse performance, she adds, as it can play a role in horses' stride length and frequency, maximum speed, and symmetry.
Conformation and genetic predisposition are risk factors for injury as well, she says, "but the advantage of footing is that it's a risk factor that we as humans can theoretically control. So if we better understand the relationship between the footing and the development of lesions, we can help prevent their development."
Studying footing isn't an easy task, according to Crevier-Denoix, which could explain why researchers have completed relatively few studies on this topic. Historically, researchers have had difficulty associating injury occurrence to particular types of footing. Other factors such as the horse's physical type, age, and training program, along with general footing maintenance--which can actually be even more important that the footing itself--could play a role as well, she says.
Researching the hoof/footing interaction in actual practice at high speeds has also presented a significant challenge. Until recently it has been physically impossible to place the research equipment on a fast-moving animal, and the equipment was not adaptable to the high stresses the equine locomotor system undergoes in training or racing conditions.
Elin Hernlund, DVM, PhD candidate in biomechanics in the department of anatomy, physiology, and biochemistry at the Swedish University of Agricultural Sciences, in Uppsala, recently conducted a footing study on elite-level jumping horses. She used high-speed cameras to measure landing speed, angles, and directions and braking speeds of each hoof as it struck, moved on, and left the ground. Her research revealed that landing speed and braking speed after a jump vary significantly from one hoof to another. But the study was limited in that she could not measure actual forces on the horse's legs and body with camera equipment alone.
"The equipment historically used for testing (mechanical weights, cadaver hooves, etc.) often does not simulate the true conditions that the surfaces are subjected to when loaded by a horse," she says. "This is a problem because footing is strain rate dependent, meaning it will respond differently depending on how fast the load is put onto the surface."
In 2007 Michael Peterson, PhD, professor of mechanical engineering at the University of Maine, built a machine designed to simulate a Thoroughbred racehorse at a gallop. While it has been useful for monitoring racetrack maintenance, the results have not yet been validated against the biomechanics of a living horse.
"The horse-surface interaction is complex; it varies between limbs (leading/trailing and fore/hind), and it depends on the horse's weight and type and the type of movement," says Hernlund. "It is challenging to build a machine that acts like a true horse."
In 2006 Crevier-Denoix, her colleague Henry Chateau, DVM, PhD, and biomechanical engineers began working with their first prototype of what has become known as the "dynamometric shoe." This special "3-D" horseshoe, nailed into a hoof like an average steel shoe, measures force in three spatial directions and the trajectory of the center of pressure. The researchers also attached a 3-D accelerometer to the hoof wall to evaluate the shock of impact and the corresponding vibrations. Combined with a high-speed camera, an ultrasound system that measures force on the superficial digital flexor tendon, and a speed-measuring device, Crevier-¬Denoix and Chateau used the shoe to quantify hoof-ground interaction at the onset of the stance phase (the period during which the hoof is in contact with the ground) and maximal limb loading at midstance, a parameter which is likely the most critical in injury occurrence.
Initially, the dynamometric shoe had to be attached to cumbersome computers via several cables, which limited the study to Standardbred trotting horses pulling a surrey. Today technological advancements have made it possible via lighter computer equipment to place dynamometric shoes on galloping racehorses and show jumping horses--even on two different hooves ¬simultaneously.
In these studies researchers are uncovering certain benefits of all-weather "synthetic" footing that traditional footing lacks, says Crevier-Denoix. "The all-weather waxed tracks (using wax-coated sand, rubber, fiber, etc.) have a 'damping effect,' " she says, meaning they absorb energy and, therefore, reduce the shock of contact between the hoof and the ground. There's also less maximum vertical loading at the midstance part of the horse's step on these footing varieties.
However, these benefits are countered somewhat by a longer stance phase, especially in the first part of the step (the damping phase), Crevier-Denoix says. This can make the footing feel "slower." And there might be side effects such as lingering tendon tension and a prolonged effort sustained by the hind limbs. She acknowledges these issues require further investigation.
This is a very important issue in the U.S. racing industry, as an increasing number of synthetic surfaces are replacing traditional ones (such as dirt), but it is also of interest for the sport horse world. Again, further investigation into these areas is needed.
Researchers are still a long way off from having the right answer for all footing situations. "There is certainly footing out there that is kinder to horses' legs, but I believe that there is no one footing that is good for all horses," says Paul McClellan, DVM, owner of the San Dieguito Equine Group Inc., in San Marcos, Calif. "With all the different conformations and foot types and ambulatory variations (the way a horse moves over the ground), one footing will suit one horse but not another."
The horse/rider combination can also affect the hoof/footing interaction, McClellan adds. "Good riders can change the dynamics with very little effort by how they sit and balance the horse," he says. "Researchers have put their heart and soul into the biomechanics of this business, but the real world reality is there are many complex challenges to it. Any great solution is going to be slow in coming."
Another challenge footing researchers face is the significant variation in biomechanical forces among disciplines. "Different sports put different demands on the performance of the surface," Hernlund says. "Grip is crucial for the show jumper, for example, but it can't be too pronounced in a surface for reining horses that need to do slide stops."
Cross-country course footing is perhaps one of the trickiest to manage. "It's hard to control the amount of rainwater on natural terrain and prevent wear on the surface," Hernlund continues. "Plus, the rooting system of the grass is crucial to prevent horses from slipping. Cross-country course designers and caretakers might have one of the most challenging situations when it comes to keeping the surface safe for all competitors."
And it would be a mistake to assume it's just competition surfaces owners and trainers should be concerned about, says Crevier-Denoix.
"On the competition ground, the horse is going to make maximum efforts, so it's clear that the quality of the ground should be optimal there," Crevier-Denoix says. "But generally speaking, musculoskeletal pathologies (tissue disease/damage) in sport horses occur over time with a buildup of training. So obviously we need to be paying attention to the footing where the horse is training every day."
Pleasure horses are subject to injury risk as well, she says, even though their training might be less frequent or strenuous. All horses worked in harness or under saddle can develop musculoskeletal pathologies as a result of inadequate footing.
Put Your Best Footing Forward
Owners and their horses can benefit from some common-sense footing recommendations: First, be aware of your horse's reactions to the footing, says McClellan. Knowing your horse well will help you recognize his comfort level on a day-to-day basis and gauge whether the footing suits him. Also, walk and jump around on the ground yourself--is it comfortable to you? If so, it's more likely to be comfortable for the horse as well. Make sure the ground drains well in rainy seasons to prevent puddles and mud, and water it well in dry seasons to avoid excessive dust.
And be sure to maintain the footing by harrowing (dragging) it regularly. "The shock of impact on a harrowed track is twice or even three times lower than on one that hasn't been maintained for several days," says Crevier-Denoix.
Above all, if you find your footing isn't right for your horse, change it. If you can't change it, McClellan's advice is simple: Find another facility with better footing. Although horses tend to adapt to the surface they travel over, they might sustain injuries along the way or not adapt at all. Don't rely on boots, wraps, and gadgets to help; if the problem is with the footing, only changing the footing will fix the problem.
If you do have the means to change your footing, don't simply rely on a good marketing campaign or word-of-mouth, and don't be won over by claims of easy maintenance, McClellan says. Check with your veterinarian and read up on the latest research as it emerges.
It might take some time before we know exactly what kind of footing our horses need. But fortunately researchers are building on these technological developments, providing the answers we need to keep equine musculoskeletal systems healthy.
About the Author
Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.
POLL: University Equine Hospitals