Written February 2014 by R.F. (Ric) Redden, DVM
The thoroughbred racehorse foot is often plagued with chronic problems, such as thin soles, weak walls, crushed heel tubules, bull-nosed or dished walls, negative PA, quarter cracks and overall lack of mass. While genetics or the rigors of training can predispose a foot to some of these issues, maintaining the foot in such a way to emphasize mass and durability can go a long way towards minimizing or eliminating these commonly encountered foot problems.
Like all breeds, thoroughbred racehorses have a wide range of foot stereotypes, all with unique characteristics that make them strikingly different from one another. Matching feet are extremely rare, and often feet on the same horse can have distinctly different profiles. These feet all have different mechanical requirements that need to be met in order to remain healthy and functional enough to withstand the rigors of training. However the traditional mindset that feet should all fall into a narrow range of norm often results in trimming, shoeing and maintenance programs designed to match feet regardless of their individual variability. Striving for the ideal image or balance, as some call it, can often be counterproductive even when all involved have the horse’s best interests at heart.
Describing the Healthy Foot
The ideal foot we have all been taught to strive for is rarely found outside of a textbook. Therefore we must reconsider the wisdom of constantly struggling to emulate something that does not naturally occur. If a foot naturally has a higher heel and steeper hoof angle than the opposing foot, rather than take it off just because it is there we should first consider why it is different from the opposite low heel foot in the first place. The internal characteristics of a foot, including bone angle, soft tissue parameters, palmar angle, etc., dictate the exterior appearance. Attempting to sculpt the seemingly out of balance exterior to meet our own perceived ideals without thought to what is happening internally often puts undue stress on internal components, which can cause inherent problems that are only compounded by the rigors of training.
In order to understand what the foot needs to be healthy, we must first understand what healthy means. It does not necessarily mean normal, as this term should relate to the unique requirements of a specific foot, not feet in general. “Healthy” is dependent on a number of variables, such as foot stereotype, breed, age, moisture content, etc., and there is not a universal standard that applies to all feet. If there was, they would all have to look alike. The belief that all feet should look somewhat the same regardless of where they fall on the large range of variability certainly deserves to be revisited.
When evaluating the health of a foot, it is important to note that the time span from the last trim or shoeing greatly influences on how we interpret balance and health. Is a foot shod for 6-8 weeks as healthy as it was when it was first shod? The following external characteristics are indicative of the ideal healthy, shod racehorse foot:
Uniform growth rings toe to heel. Rings form approximately 30 days apart and have a wide variety of patterns and characteristics. All feet have growth rings and none are pathognomonic for specific disease syndromes, e.g. prominent growth rings and diverging rings are often mistaken for founder rings. Caution is due as the history, radiographs and clinical findings must support the diagnosis of laminitis. Growth rate variations, other syndromes and injuries also result in prominent and diverging growth rings.
Natural front toe angle approximately 52-54° with less than 5° disparity between opposing feet (depending on a 50-51° bone angle, which can vary considerably).
Heel angle within 15° of toe angle. Others have advocated heel angle should be within 5° of toe angle, otherwise they are considered underrun. I strongly disagree, as this simply doesn’t occur in the extremely large population of thoroughbreds I have observed and worked with across the horse world.
Good growth rate that produces enough hoof length to almost trim off the last set of nail holes. This translates to approximately 10-15mm over a 30-45 day period. Note that growth rate is influenced by weather; in the winter months the hoof is more dormant than it is during warmer months. Trim schedule, exercise, stereotype, environmental conditions, age, disease and injury can all affect growth rate, therefore it is important to be aware of these factors. Healthy feet with slower growth rate can normally have an extended shoeing cycle. Note distance between growth rings, toe to heel and medial to lateral.
Face of the hoof is relatively linear, void of dish or bull nose and not influenced by the rasp.
Heel height (hairline to ground) is relatively the same between opposing feet.
Linear pastern/hoof alignment in a slightly offset plane.
Relatively smooth hoof surface void of surface cracks and horn defects.
Clinches tight and well set even when shod 4-6 weeks (which indicates low water density and horn rigidity).
No overgrown quarters hanging over the shoe during a 30-45 day shoeing cycle.
Strong, full thickness wall slightly longer than sole.
Strong bars untouched by knife.
Good sole mass with cupped or flat sole (as long as it has mass).
Wide, strong frog at ground level or slightly deeper within the foot.
Heel tubule ground surface contact reasonably close to the widest part of the frog.
Medial/lateral frog sulci of equal depth (medial/lateral balance).
Medial/lateral equal growth rate (note ring gaps).
Radiographic characteristics (on a lateral view taken with Redden low beam orientation):
Relatively uniform horn-lamellar (HL) zone (influenced by hoof and bone shape) with variable range of 15-25mm, dependent on age, breed, weight, foot size and lineage. This range is based on examination of several thousand feet, however this range may be much larger among a larger population of thoroughbreds.
Lamellar zone relatively parallel.Positive PA of 3-5° regardless of bone angle.
Relatively linear palmar rim void of apex erosion, remodeling and the scalloped appearance that is often observed along the central palmar surface.
Minimum 15mm sole depth under the apex, preferably 20mm or more, with a slight natural cup at trim or reset time.
CE can range from a few millimeters up to 15-20mm on sound feet, relative to stereotype and degree of DDFT tension (high/low syndrome). The largest CE observed by the author on a sound warmblood was 35mm.
Digital breakover distance will vary due to foot mass and toe length.
Minimum soft tissue parameter disparity between opposing feet.
One branch of the palmar rim (medial/lateral wings superimposed).
Radiographic characteristics (on a DP view taken with Redden low beam orientation):
Medial/lateral palmar rim relatively parallel to the ground surface, and of more importance, digital articular surface uniformity.
Even depth sulci.
Relatively symmetrical medial/lateral palmar zone bone shape.
Relatively equal medial and lateral bone mass.
Apex visible slightly distal to wings (positive PA).
While these characteristics describe the ideal foot, most feet unfortunately fall outside of these parameters to some degree. However they can remain quite healthy and sound as long as all components (suspension and support) remain in harmony and have natural recall. Be careful not to limit the range of norm when considering balance. What is a healthy, quality prepared foot for one horse may be trouble for the next, and this goes for feet on the same horse. Most all horses have some variation of the high/low syndrome: one foot will have a higher profile than the other, which in the author’s opinion reflects one of four basic grades of the club syndrome. They the same on the inside, therefore they will not be the same on the outside, and forcing them to match will inevitably create unwarranted problems.
It is important to keep in mind there is a remarkable range of variability, and often disease and/or injury can result in hoof capsule distortion and soft tissue parameter alteration to some degree. However if the insult to vital growth centers has not damaged the nutrient supply to these areas, evidence of a previous problem may not be demonstrable.
The racehorse seldom meets this ideal standard and most all horses in training will fluctuate up and down the scale relative to many factors that are influenced by genetics, conformation, nutrition and farrier and trainer perceptions of what each foot requires. Veterinarians’ perception of the ideal image may be somewhat different from that of the farrier and trainer. Daily maintenance requirements, bedding, exercise, demand for toughness and low moisture content also play a role in the overall level of health of the foot.
The key to a healthy foot is mass. Trying to establish a well-balanced foot without mass is often counterproductive, as without adequate foot mass to protect the underlying sensitive structures, a foot that is balanced can still be considered borderline at best, unhealthy and vulnerable to injury. Therefore trimming, shoeing and maintenance protocols should be geared towards promoting tough, durable feet with good foot mass (sole, frog, horn and digital cushion) and a slightly positive PA. From day to day care provided by trainers and grooms to routine vet and farrier care, we can determine a foot’s individual needs and design a plan accordingly.
When presented with less than optimum mass and balance (medial/lateral to anterior/posterior relationship), our task is to detect the weak area and make a quick assessment of how we can mechanically enhance the natural recovery process, all the while being mindful of internal variations. Doing so at the earliest sign of deteriorating horn matrix offers the largest window of response, allowing us to prevent or at least manage the heel crushing, tubule folding syndrome that haunts an alarming number of racehorses.
Farriers worldwide have been unjustly accused of taking the heel off of horses with the long toe/low heel appearance. This is not actually the case however, as other factors contributed to the demise of the heel. The farrier simply removes dirt and frayed, crushed tubules hoping to find solid heel to set the shoe to. This is not a problem with your farrier, but a problem for your farrier. Backing up toes to seemingly correct the long toe/underrun heel foot may appear to make the heel take on a more balanced relationship with the ground. However the toe only appears long because there is no heel. I see a lot of healthy toes and no heel, and therefore do not endorse the long toe/underrun heel theory.
Let’s look at the typical yearling foot going into training. Those managed with an ideal foot program and management team will have strong hoof capsule with mass and robust heels whether shod or barefoot. Once confined to a stall 23 hours a day vs turnout, the foot loses demand for toughness. Standing in straw, shavings or paper bedding seems to be the way to bed horses, however they are on their feet the majority of the time and the super soft footing further reduces demand for toughness.
When training begins the feet naturally heat up, as do muscles and joints. Then the mud bucket comes out and the feet are packed almost daily to remove heat. The mud dries quickly for the first few days, but then remains moist once the hoof capsule has the same water density as the mud through osmosis. The heat is gone, but unfortunately the strength, rigidity, and recall of all support components have been compromised.
I have often encouraged trainers to take photos and baseline lateral and DP foot radiographs of young horses coming into training and observe how quickly the heel begins to crush along with the deteriorating internal balance. Being aware of the dramatic changes early on can greatly help us slow the process and minimize the effects of the heel crush syndrome provided trainers, veterinarians, farriers and caretakers are all on the same page and well aware of the unique characteristics and requirements for each foot under their watchful eye.
Once the cycle begins, several major support components fail simultaneously. As the heel angle decreases, so does digital cushion mass. As cushion mass becomes compressed, shock absorbing abilities are greatly reduced, passing excessive load to the heel tubules, which quickly fold inward and forward. As the heel tubules fold the bars do likewise and they lose their strategic shape and location, which is strongest when quite close to the widest part of the frog. The domino effect puts tremendous pressure on the vascular supply controlling growth centers and these vital components, compressing it throughout the horn, cartilage and lamellar attachment. This causes a decrease in toe angle and PA along with sole mass, especially in the heel area. The steeper profile foot may begin to dish and the opposite can develop a bull nose appearance, especially behind. The heel bulbs become remarkably asymmetrical. The medial frog sulci become quite shallow as the heel bulb is pushed more proximal. This is a very misleading external alteration that can be quite confusing to the farrier when they try to balance a foot using the heel bulbs as a reference point.
These alterations may not elicit a specific pain response, however as the cycle continues cumulative damage contributes to soreness throughout the heel area. All structures, including the articular surface, are inflamed due to a lack of natural shock absorbing protection to sensitive components. Quarter bruising followed by a quarter crack often results, along with numerous compensating soft tissue and bone injuries that can and far too often do cause catastrophic, crippling or fatal injury.
How do we prevent, slow or reverse the cascading series of events?
Be alert to the characteristics of a strong, healthy foot, all the while being aware of the large scale of internal variability in high and low profile feet both front and behind, visibly and radiographically.
Learn to enhance the strong areas and strengthen weak areas. They will continually change and require astute attention from all concerned.
Keep the feet dry and tough. Excess water destroys horn durability and natural recall. Stop and think about what happens to your toenails after soaking for only a few minutes in a hot bath. Throw away the mud bucket.
Maintain optimum mass of sole, frog cushion and horn.
Remove only what the foot doesn't need and leave nothing that is harmful. Backing up toes to make the heel appear stronger is not a productive procedure; it is not that the toe is too long – the heel is gone. Backing the toe up to make the heel appear stronger simply perpetuates weakness.
Maintain full thickness horn wall at ground or shoe surface.
Leave maximum frog depth and width. Remove only tags and areas that catch and harbor moist debris.
Remove only flaky sole. Leave maximum sole depth. It will not get too thick or too protective. Shoes create painful pressure on shallow soles, while thick, durable soles thrive on it. Therefore shoeing requirements for the shallow foot are quite different from the robust, durable foot.
Touch the bars only very lightly if they appear weak and fragile. Otherwise leave them strong and full thickness.
Trim to emphasize a positive PA when it is 0° or negative, especially in hind feet. This may call for shoe design that is anything but flat.
Hind feet often drift into the negative zone with only few resets as training, speed, hours of inactivity and low or no demand on horn and excessive moisture steadily destroys mass, balance and overall integrity of the foot. This is not a problem with your farrier – it is a problem for your farrier.
To prevent this inevitable negative PA development, strive to trim the ground surface to a positive PA every single time. Of course this is dependent on how much you have to start with. Take all you can from the widest point of the foot forward, then take a little more, especially behind. Always be aware of the overall foot mass. The appearance of hind foot sole may lead you to believe you cannot take any more. Work off of lateral x-rays as often as possible to learn what you have to work with and what you have left. Avoid nippers, as the preconceived idea of how much foot needs to come off can compromise our efforts once we discover we need more foot after it is already gone. The rasp allows for more flexibility depending on what we find as we remove excessive horn and the end goal.
Tips for preparing the foot for the shoe:
Be reasonably certain of the PA and sole depth under the apex. You can only learn this by observing the relationship of external landmarks with radiographic soft tissue parameters.
Avoid trimming all feet to look alike with a textbook profile. This can drastically disrupt natural balance instead of enhancing it.
Avoid trimming out live sole, bars and frog before removing wall. This practice encourages you to remove more sole than is necessary, which is followed by removing more wall than is necessary.
Avoid trimming from toe to heel in a flat plane when heel crushing is present. This invariably lowers PA, creating more of the same with each reset. Consider shoe modification that offers a positive PA and less heel crush benefits.
Avoid use of nippers when there is less than 8-10mm of horn wall to remove. You are committed for another 4-6 weeks when the foot is suddenly on the ground and you will have a tendency to follow the wall that protrudes above the freshly trimmed sole.
Many traditional trims are designed to take all that is possible instead of leaving all that is protective. Over trimming the sole makes the wall appear excessively long, therefore far more wall is removed than necessary. The wall is nipped off, then lowered even farther by the rasp. This makes the sole look too flat, so it is cupped, once again with the knife. As the frog now appears to be too large it is also taken down with the knife. Now the best part of the foot is on the ground for the dogs. Does this sound familiar? We have all been there. If you want to see stronger, healthier feet then we must have a totally different perception of what we want it to look like when we are finished and what we want to see in 4-6 weeks. Study these tips and try to spend more time observing what is needed instead of removing foot and nailing on the shoes.