More Hoof Ideas from Dr. Robert Bowker
by Yvonne Welz ©2007, as published in Issue 27 of The Horse's Hoof Magazine
Yvonne Welz with Dr. Robert Bowker.
James & I attended Dr. Robert Bowkers 2-day clinic in January, 2007, which was part of the Easycare-sponsored Pete Ramey & Dr. Bowker event. Though I had read about Bowkers work for years, I had not grasped the scope or complexity of it, nor did I realize how compelling his collected evidence in support of barefoot is. THH Issue 26 included my quick summary of what I felt were some very intriguingand controversialpoints presented by Dr. Bowker. I hoped to whet peoples appetite, and spur them to find out more about what this amazing researcher has been doing.
Now I will attempt to delve deeper into my interpretation of what
I saw presented by Dr. Bowker. Please read these ideas with an open mind, and
understand that this is my perception. While you can disagree with interpretations
and conclusions, they do not detract from the content of the actual scientific
studies, which should really be examined first-hand.
Who is Dr. Robert Bowker?
Robert Bowker VMD PhD is a Professor of Anatomy and Director of
the Equine Foot Laboratory at Michigan State Univ. College of Veterinary Medicine.
His most important role (to us!) is that of veterinary researcher, and through
funding support from the AQHA and Grayson Jockey Club, Bowker has been able
to spend the last decade and a half studying the function of the equine foot.
Much of his research has been on the microscopic level, and through the dissection
and study of literally thousands of cadaver hooves.
The All-Important Back of the Foot
The rear of the hoof is possibly THE most important area for determining
the health of the hoof. Bowker remarked that he kept trying to look elsewhere,
but no matter what he did, it all kept coming back to the rear of the hoof!
The back of the foot is exactly where three of his most well-known
studies have focused. The first was his hemodynamic flow theory, which proposes
that blood flow through the network of tiny capillaries in the heel region plays
a vital role in shock absorption of the hoof. Second was his discovery of proprioreceptor
sensory cells in the heel region; these cells may transmit information to a
horses central nervous system and allow him to feel his way
across the ground. And third was his study presenting the differences hes
discovered between a good foot and a bad foot.
Bowker realized that previous work on hooves did not differentiate
between healthy and unhealthy feet, so he set out to change that. In his cadaver
studies, in horses under the age of 5, the back part of the foot looks the same.
But after the age of 5, horses soon begin to split into two different groups
that are easily identifiable. The good-footed horses developed fibro-cartilage
in the digital cushion area of their hooves; while the bad-foot horses do not
develop fibro-cartilage, and their digital cushions remain fatty connective
In the good-footed horses, the digital cushion is completely transformed
into a very strong fibro-cartilage. It is clear that the horses were not born
with this fibro-cartilage; rather, the tissue is stimulated (through movement),
and the fibro-cartilage is created through this stimulation. Bowker is convinced
that the horses early years are crucial for the development of the hoof,
and only movement can create this crucial structure. Once the fibro-cartilage
is created, it appears to be permanent. In addition to this fibro-cartilage
in the digital cushion, a good foot also has thick lateral cartilages (3-4 times
thicker), well-developed microvessels, and fibro-cartilage in the center of
A good foot will also tend to land slightly heel-first, which
activates the proprioreceptors in the heel, stimulates the blood flow and allows
for hemodynamic shock absorption. A toe-first landing is the sign of a sore
A bad foot is not genetic; the horse was simply unable to adapt
to improper load, negative stimulation, or inadequate environment. And, there
is still hope for the older bad-footed horse. The cells to create the fibro-cartilage
are still there, so the theory is that they can be activated through stimulation
at any age, though no studies have yet confirmed this.
The Concept of Peripheral loading
Peripheral loading occurs when the edge of the hoof (hoof wall)
bears more of the weight load. Peripheral loading always occurs with shoes,
since they focus the weight upon the hoof wall. A shoe can therefore be called
a peripheral loading device. However, peripheral loading can also occur with
barefoot trimming, if the trim places more of the weight upon the wall. Over-trimming
hoof structures such as the frog, sole and bars, so they have no possibility
of sharing in the weightbearing load, will tend to create more peripheral loading.
Allowing the hoof wall to grow too long will create more peripheral loading.
Anytime the frog is not in contact with the ground, peripheral loading takes
place. To make things more complicated, peripheral loading is completely dependent
upon the hoofs surfacea hard surface increases peripheral loading,
while a softer surface decreases it. A solar plug (material packed into the
hoofs concavity) minimizes peripheral loading.
Peripheral loading is a negative situation for the hoof, because
it severely interferes with blood flow inside the hoof. Bowker conducted experiments
in velocity of blood flow in the hoof using Dopplar Ultrasound. What he discovered
is that harder surfaces made the blood flow faster, and when it did that, it
never perfused the tissues. It was just like a rainstorm in the
desert (and Ive seen plenty of those!)water gushes down in a flood,
but never sinks into the ground. The faster the blood flow, the less blood made
it to the tissues!
On softer surfaces (pea rock, sand or foam pads) blood flow
will slow down and trickle through small vesselsmicrovenous vessels. On
hard surfaces (cement or wood blocks), tissue perfusion dramatically decreases,
so blood moves faster through footit must stay in the large vessels. Different
surfaces will change tissue perfusion, with softer, more forgiving surfaces
having the greatest tissue perfusion.
He also documented the effects of more extreme peripheral loading.
With a shod hoof, blood flow actually came to a halt for a split second with
every heartbeat, at the level of the horses fetlock. In a computer model
that he developed with some engineers, he measured stresses on the coffin bone,
and discovered that a peripheral load encouraged bone to be removed. A solar
load encouraged bone to be laid down, or at least not removed.
The Responsiveness of the Hoof
The horses foot changes throughout its life. All four feet
of a horse are different from each other, due to environment, exercise, trimming
and active stimulation of the foot. And even wild horses hooves are all
different, which makes it impossible to use them as a gold standard. There is
no one wild horse model.
The horses foot is incredibly adaptive! It is only when
its ability to adapt is exceeded, that lameness shows up. Amazingly enough,
laminae are created in response to stress. The hoof is constantly adapting to
stresses in the environment, and it appears that more laminae actually develop
in the areas of stress inside the hoof. Fewer laminae are better, and extra
laminae are signs of stress (they become thinner and longer, with a greater
chance of laminitis). It has not yet been confirmed, but shod horses may have
more laminae than barefoot horses. However, shod horses with toe clips do have
more laminae around these clips. (This means we can mechanically increase the
density of laminae!) Horses, in general, have more laminae on the flared side
of their hooves, and more laminae at their toes. There are also more laminae
in front of a sole callous; the pillar edge of a sole callous appears to be
a stress area.
Not only are laminae created in response to stress, but it appears
that hoof horn is, also. More about this later, but it appears that hoof tubules
actually change direction according to load and stresses in the hoof wall.
The hoof is so responsive that there is a change in the physical
contact area of the hoof between standing on concrete and standing on rubber.
The hoof wall is fluid; hard but will actually move. There is a little more
surface area of the hoof when the horse stands on hard rubber versus concrete,
and this drastically reduces the pressure inside the hoof capsule. There is
only 1/3 the amount of pressure on the hoof wall when standing on rubber versus
standing on concrete.
The Necessity of Movement
Over and over again, we kept coming back to the importance of
movement for the health of the foot. While this has long been a constant theme
for natural hoof care, it was nice to finally have some science that backed
this up! Bowker gave one clear reason why movement is so important: it improves
the perfusion of the foot. This was readily measurable in his blood flow studies.
Movement is also the only way the horse can develop the fibro-cartilage in the
back of the foot, so a young horse without freedom of movement is a young horse
destined to develop into a bad-footed horse!
Bowker has also taken his study of movement out into the field.
Using very expensive and sophisticated pedometer devices, he measured the movement
patterns of groups of horses living on 2-3 acre plots, and discovered that most
healthy horses averaged about 4,000-6,000 steps per 24-hour period (3-5 miles).
In contrast, horses living 24/7 in a stall took about 800 steps per day.
How the Hoof Grows
Walls: This seems obvious once you think about it, but for some
reason, it had never been explored before Bowkers studies. The hoof is
shaped like a cone; the hoof is greater in mass distally than proximally. Either
there are more cells at the bottom of the hoof, or the cells got bigger! Well,
they didnt get bigger. So Bowker wanted to find out how and why there
were more cells at the bottom. He consulted with a specialist to record cell
mitosis (cell division) in the hoof, and discovered there is no significant
mitotic activity below the coronet. This is consistent with Dr. Chris Pollitts
work. There are more cells, but where did those cells come from?
It turns out that the hoof wall does not simply grow straight
down from the coronet. Most of it does originate from the coronet, especially
the hard outer wall, but at least 1/3 of the wall is created from laminae-derived
tubules. The secondary epidermal laminae carry little grocery bags
of cells with them, and as they descend the hoof, these cells can go wherever
the stresses are.
Bars: It has been previously assumed that the bars were structurally
identical to the hoof wallthat they were simply an extension of the wall,
turned around the frog. That doesnt seem to be the case! The laminae of
the bars are different than the laminae anywhere else. The bars laminae
seem to be able to form tubular horn and contribute to both the wall and the
sole. Bowker has been studying this on a microscopic level, and observed that
tubules formed from the bars, grew forward, and migrated towards the toe. Bowker
now believes that a significant amount of the sole might be coming directly
from the bar laminae. Note: the bar laminae are contributing keratin cells to
the sole, and so are the laminae (when well-attached). The solar corium does
contribute sole, as well.
The Function of the Laminae
If the laminae are responsible for providing tubules to create
at least 1/3 of the hoof wall, and the wall is fluid and dynamic, it starts
to become questionable as to whether the laminae are actually a support structure
for the hoof. Bowker now believes that the idea that laminae form the suspension
that holds the horse up is false. He says that there is no direct connection
that can be shown between the laminae and the coffin bone to indicate support.
He compared it to saying that your hand is attached to your shoulder: true,
but there is a lot of tissue in between!
Instead, Bowker theorizes that the function of the laminae is
keratinocyte (keratin producing cells) storage, and producing tubules for the
white line and sole.
Pea rock: Horses (especially laminitic horses) love pea
rock, which is a small, smooth, round river rock. Bowker recommends 3-6 inches
of pea rock, on top of sand base. While horses may stand with their toes down
in pea rock, their weight is actually on their heels. In his blood flow studies,
pea rock created the highest blood perfusability rating.
Substance P Receptors: The sensory nerves in a horses
foot are there for more than just pain; the nerves secrete a potent vasodilator
called Substance P. Substance P acts on the small blood vessels
in the foot. In the navicular horses he studied, the Substance P receptors are
gone! The Substance P receptors were destroyed, and therefore there are less
blood vessels and a loss of blood flow regulation. The decreased blood flow
leads to remodeling of the bone. Navicular horses have lost the ability to control
blood flow through the foot, due to the loss of these receptors. When a horse
has lost the Substance P receptors, we end up in a catch-22 situation: the hoof
cant heal until blood flow improves, but the blood flow needs the Substance
P vasodilator to improve!
Pulsating Veins: The veins in a horse pulsate. This is
a unique feature of the horse, and something that has not been acknowledged
before. Veins of the distal limb of the horse have extensive musculature
around them, and this smooth muscle appears under neural control. The vein pulsates
like an artery! However, in a laminitic horse, the venous pulses become
less distinct and less consistent.
In regards to Dr. Bowkers description, The hoof wall
inside is like peanut butter. This one item probably got more comments
of disbelief than any other, because so far no one has seen any peanut butter
when dissecting a hoof. Not only was Bowker describing the inner wall, with
its softer texture, but also I think he used this analogy to make a strong point:
the hoof is changing, fluid and malleable, and NOT a rigid structure.
Everything we learned at Bowkers presentation totally reverberated
with us. We discovered new ways to think about the old familiar concepts and
we acquired new tools to communicate these concepts to clients. How great is
it to have an easily explainable scientific explanation for why shoes are best
avoided? (just define peripheral loading!)
Note that Bowker is not a professional trimmer! His research does,
however, provide us with a wealth of guidance. Trimming needs to be done as
frequently as possible to minimize peripheral loading effects. Excess hoof growth
will exacerbate peripheral loading. One of the best trimming tools for minimizing
peripheral loading is the mustang roll, because it relieves the pressure on
the outer hoof wall.
Bowker is a big advocate of backing up breakover on hooves: Short
toes are the best thing you can do to a foot! His simple recommendations,
which he calls the Physiological Trim, are short toes, short heels, and trimming
for the 1/3-2/3 balance of the foot: 1/3 of the foot in front of the apex of
the frog, and 2/3 behind it.
To create a thicker hoof wall, shorten the toes. To fix an underrun
heel, shorten the toes. In an insulin-resistant horse, the inside of the hoof
wall is actually unstable (keratinocytes are migrating more), so to compensate,
reduce load on the hoof wall (short toes and mustang roll). Note: Bowker is
against thinning the sole at the toe from the bottom, so flared toes should
be backed up from the front only.
Clarification on bar trimming: Some people have taken Bowkers
recommendation of weight-bearing bars a little too much to heart, going so far
as to discontinue all trimming of bars on all horses. I clarified this with
himwhen he talks about weight-bearing bars, he means the rear of the bar
being weight-bearing upon impact. He said that he very much believes in concavity
of the hoof! So if a bar needs trimming, it needs trimming. Bowker is, however,
very much against excessive removal of the bars, i.e. trimming them to the point
where they no longer function as a weight-bearing structure. The bars need contact
with the ground for correct blood flow and sensory stimulation. (And remember,
terrain matters, so a horse on deeper terrain would receive more contact with
shorter bars, and vice versa.) Since the bars are responsible for some of the
sole growth, they should not be removed. He also recommends that the soles should
not become flat, but should have concavity, with a thicker sole if needed.
Believe it or not, there was much more, but weve run out of space in this article. In Bowkers presentation, there is a great deal more detailed technical and scientific information, and photos, charts and data from many of his studies. He goes into much greater detail about his hoof growth and navicular studies. But dont just take it from me, attend a Bowker presentation and evaluate his information first-hand.
Dates for Bowker seminars are listed on Pete Ramey's website: http://www.hoofrehab.com
As published in Issue 27 of The Horse's Hoof Magazine
More info about Dr. Bowker:
NEW! Highlights from the Tucson Clinics: Pete Ramey, Dr. Robert Bowker, and EasyCare Inc. (2007) by Yvonne Welz, from Issue 26 of The Horse's Hoof Magazine
Robert M. Bowker VMD, PhD,
Professor of Anatomy, Michigan State University College of Veterinary Medicine
Equine Foot Laboratory website: http://www.cvm.msu.edu/RESEARCH/efl/index.htm
Scientific paper: The Growth and Adaptive Capabilities of Changes in Response to Stress (21-Nov-2003) pdf file
Scientific paper: Contrasting Structural Morphologies of 'Good and 'Bad Footed Horses (21-Nov-2003) pdf file
Press release from Michigan State Univ., Physiological
Trimming for a Healthy Equine Foot (.doc file)
©2007 by The Horse's Hoof. All rights reserved. No part of these publications may be reproduced by any means whatsoever without the written permission of the publisher and/or authors. The information contained within these articles is intended for educational purposes only, and not for diagnosing or medicinally prescribing in any way. Readers are cautioned to seek expert advice from a qualified health professional before pursuing any form of treatment on their animals. Opinions expressed herein are those of the authors and do not necessarily reflect those of the publisher.
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