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).