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We will improve these graphics as soon as possible, but this article will hopefully help you to see a healthy non-laminitic foot (top) compared to a chronic laminitic foot (middle) or a laminitic foot that is showing risk factors associated with P3 penetration of the sole (bottom).   
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DRAFT The deep digital flexor tendon (DDFT) pulls upwards from its insertion site on the back of P3, with traction from wrapping around the navicular bone, and pushes the toe downwards. The force on the toe is increased when the toe is long. For active flexion of the DIP joint, the deep digital flexor muscle contracts, and this increases tension in the DDFT. Flexion of the DDFT is opposed by contraction of the common digital extensor muscles and the common digital extensor tendon, which inserts on the extensor process of P3. The DDFT lifts the palmar aspect of P3 and thereby moves the centre of pressure forwards (towards the toe) in relationship to the centre of rotation. Palmar rotation of P3 and having chronically high heels may lead to shortening/contraction of the DDFT. DDFT tension changes in horses with chronic laminitis, and pain from laminitis may also lead to changes in DDFT tension. Prolonged tension on the DDFT may contribute to reducing lamellar perfusion and increase shear forces on the dorsal lamellae. Ramsey et al. 2011 found, in an in vitro study, that elevating the heel up to 15 degrees might increase shearing forces on the dorsal lamellae. A deep digital flexor tenotomy - cutting the deep digital flexor tendon (DDFT) - is sometimes recommended following laminitis when correct realigning trimming and support fails to realign the feet. There are two recognized procedures - the DDFT can be cut either: 1. at the mid-metacarpal (the middle of the back of the canon bone) - less risk of complications, but less release of tension in the tendon is achieved, and possible risk of metacarpophalangeal joint (canon bone to P1) contraction; 2. at the palmar pastern (the back of the pastern) - increased risk of complications e.g. DIP joint subluxation, but also increased release of tension in the tendon. DDF tenotomy is indicated in horses that have chronic phalangeal/bony rotation, i.e. a line through P2 and P3 is broken forwards, the distal interphalangeal (DIP) joint is abnormally flexed, and the palmar angle is higher than normal (>10 degrees), and correct realigning trimming to slowly lower the heels (without removing sole depth in the front of the foot if sole depth is insufficient) has been attempted but caused the horse to raise the heel (In this case, before considering a DDF tenotomy, ask whether the heels could have been lowered too quickly, replace heel material lost with padding, and if the horse can be made comfortable, try again to very slowly lower the heels, possibly aiming for 5 or more trims to lower the heels, and possibly making the initial aim (at the end of the 5 or more trims) around 8-10 degrees rather than the usual 3-5 degrees following laminitis). In some cases the fetlock joint may be abnormally flexed forwards with the horse walking on the toe of the foot, unable to lower the heels to the ground, even with abnormally high heels. DDF tenotomy is not suitable for horses that have a negative palmar angle, or where lamellar connections in the back of the foot are compromised. The back of the foot should be stable before considering a DDT tenotomy. Complications of DDF tenotomy include:
Opinions vary on how to manage the foot following a DDF tenotomy, and depend on which tenotomy method was used. The back of the pastern tenotomy gives a greater release of tension in the DDFT but also creates increased instability in the DIP joint. Applying a shoe or device with a raised and possibly extended heel is recommended to prevent subluxation of the DIP joint. Some vets recommend a shoe or device with a raised and possibly extended heel following the mid-cannon tenotomy as well. Pressure wraps over the canon bone and long-term box rest (up to 3 months) may decrease the amount of scar tissue formation and thickening of the DDFT and reduce the risk of metacarpophalangeal joint contraction. References:
Ramsey GD, Hunter PJ, Nash MP The effect of hoof angle variations on dorsal lamellar load in the equine hoof Equine Vet J. 2011 Sep;43(5):536-42. doi: 10.1111/j.2042-3306.2010.00319.x "The models in this study predict that raising the palmar angle increases the load on the dorsal laminar junction. Therefore, hoof care interventions that raise the palmar angle in order to reduce the dorsal lamellae load may not achieve this outcome." DRAFT What are the benefits and disadvantages of barefoot v shod for horses recovering from laminitis? For laminitis rehab, TLS doesn't recommend shoes because: feet usually need frequent trimming during realignment - heels can grow 10 mm in 3 weeks, and shouldn't be lowered by much more than 10 mm, so trims usually need to be no more than 2 weeks apart initially until the feet are fully realigned. the walls are not fully connected to the bone (and therefore skeleton), so weightbearing on the walls should be minimized. This is particularly important when an area of separation can be seen on the x-rays, as nothing in front of the area of separation is stable and therefore shouldn't bear weight at all. - the horse needs support directly beneath the pedal bone. if the sole is thin but there is palmar rotation, i.e. heels need to come down, the only way to do this is to trim the bottom of the foot in 2 planes, impossible with shoes, no problem with well padded boots. nearly all the penetrations we've seen have been in horses wearing shoes with no sole support (I have to say with the exception of the penetration we're working on at the moment, but she had casts fitted around pads with a hole cut out beneath the tip of P3 in the pads, giving P3 a hole to fall down into, which is exactly what happened. We think the only reason only 1 foot penetrated was because the hole in the pad on the other foot was badly placed and not beneath the tip of P3). We see a lot of horses fail to recover, or P3 penetrate the sole, when they are wearing heart bar shoes, either plastic or metal. Some examples: Horse&Hound Forum 2010 A 14 year old 16 hh mare had been suffering from laminitis for 10 weeks when she suddenly deteriorated and the pedal bone could be seen as a bulge in her sole. X-rays were taken and confirmed severe rotation in both back feet with around 1 mm of sole covering the pedal bone. Front feet were not affected. Imprints were fitted and eased her discomfort, after which pain was only seen when she walked out of the stable. On between 4 and 1 Bute a day, not tested for PPID (or insulin?). Mare described as always having sensitive/thin soles. 3 days after posting on a forum for help, the owner reported that the mare had been unable to put any weight on her worst foot, the bone had moved more and sunk and vet and farrier said there was no alternative but to PTS. Lessons to learn: X-rays should have been taken as soon as laminitis was suspected - ideally on the first day, and definitely within the first week - and the feet realigned and supported through the full solar surface. Horses should not leave their area of confinement with wall to wall bedding until their feet are fully realigned, well supported through the full solar surface, and they are off of all pain relief. Lifting a horse off of its soles will often reduce pain - but is also likely to leave the pedal bone unsupported, allowing actual solar penetration. Shoes will load the walls - already disconnected from the bone - and not allow lowering of the heels but protection of sole depth in the front of the foot. The cause of the laminitis must be identified as soon as possible and removed/treated/managed. Although very limited, research by Panagiotopoulou et al. at the RVC that looked at the effects of a steel shoe v no shoe on one TB gelding when walking over a platform, found that "in all cases, the shod horse showed higher concentration of stresses on the P3 than the unshod condition, with the caveat that none of these differences were statistically tested." Panagiotopoulou O, Rankin JW, Gatesy SM, Hutchinson JR A preliminary case study of the effect of shoe-wearing on the biomechanics of a horse’s foot PeerJ. 2016;4:e2164. doi:10.7717/peerj.2164 Following laminitis horses can develop separation at the coronary band with drainage of fluid that may be bloody or clear serum. In severe cases the whole hoof capsule can slough and become loose and even come off completely. Hunt RJ Equine Laminitis: Practical Clinical Considerations AAEP PROCEEDINGS Vol. 54 2008 Hunt suggests that "when steroid-induced laminitis does result in displacement of the coffin bone, it is generally severe and may result in sloughing of the hoof capsule in a matter of days to weeks." Detachment of the hoof capsule may also be seen in horses with sepsis-related laminitis within days to weeks. "There are some extreme cases where sloughing of the entire hoof capsule is inevitable, facilitating the removal of the detached hoof capsule seems to bring relieve but nothing to nail or glue on to! Deep bedding, good bandaging and nursing can tie these patients over till they have grown a new hoof capsule back, a process which goes much quicker then one would expect." See photos in link: Hans Castelijns, farriery.eu Hoof pulled off, loss of entire hoof capsule - horsesidevetguide.com "Hoof sloughing can and does occur in more severe cases. Experience has shown that equines 14 hh upwards are more likely to succumb to this complication, due to carrying sufficient weight to more readily tear through the hoof. With such cases a second crisis period, post-acute stage, anywhere between two to four months into recovery is not uncommon. This is when the hoof capsule is sloughing but the new hoof has yet to regenerate and may be less than a quarter grown." Treatment of Laminitis - Andrew Poynton, imprintshoes.co.uk
Cases where horses recovered from hoof sloughing The Helpful Farrier: Dimpled Laminitis Treatment Stirs Facebook Furor and Charitable Shoeing - Fran Jurga, hoofcare.blogspot.com July 2013 Shows a photo of a laminitic foot (A month after receiving medical support...), with a line "where the mare had tried to slough her foot before she received treatment". Case Report: Laminitis - Life Data Labs Inc. The hoof walls sloughed off of a 13 year old Quarter Horse with severe laminitis. The horse made a full recovery and had returned to his previous level of work 18 months later.  Case Report: Laminitis - Life Data Labs Inc. The hoof walls sloughed off of a 13 year old Quarter Horse with severe laminitis. The horse made a full recovery and had returned to his previous level of work 18 months later. Farriers and trimmers often worry about shortening the toe on a horse with dorsal rotation, thinking it could cause pain. These diagrams hopefully explain why it doesn't....  Above: The only nerves and blood vessels in the front of the foot are in the coriums that surround P3 - shown by the thick pink lines. The hoof to be trimmed is marked in yellow, the hoof to protect and grow is marked in orange. You can see that the pink area falls wholly within the orange area where we need to protect the foot, and nowhere near the yellow area where we want to trim the foot. The only exception to this is where the tip of P3 has some bone remodeling - there does appear to be a bit of remodeling on this x-ray - so allowing a slight margin for this is sensible, but even allowing for a decent margin around the tip of P3, the yellow trim lines aren't near the corium/tip of P3.  Above: This diagram shows a drawing and dissection of a laminitic foot (left) against a healthy foot (right).  Above: The same coloured lines are marked on the diagram and photo of the laminitic foot to show how the trim doesn't go near the nerves and blood in the laminar corium: Inner pink line = dorsal surface of P3. Outer pink line = outer edge of dermal laminae and edge of sole at ground level. White line = outer edge of white line (which is the outer edge of the epidermal laminae), being around 3 mm to the outside of the true edge of the sole. Red = true toe - runs from the hairline at the toe to the ground, parallel to the dorsal surface of P3. Purple = breakover bevel to reduce separating forces on the toe. Ideally this will start at or just to the outside of the edge of the true white line, so 3 to 5 mm outside of the true edge of the sole.  Above: Note we talk about the "true" white line and sole, as the true white line and sole can be covered over by sole/laminar wedge material, as on this foot with a solar penetration below, taken around 2.5 months after the sepsis-related laminitis event - so the foot has had time to change/grow abnormally. The x-ray and sole photo are lined up reasonably well (but not exactly). The position of the tip of the pedal bone can be seen outlined in green (this may be very slightly in front of the tip of P3 - it's the opening in the sole where the tip of P3 appeared a couple of weeks later (presumably because the foot was not correctly realigned and supported)). Brown - the frog apex may have grown very slightly forwards - but also may not have done - the true frog apex should be checked on the foot. This provides a good guide, as approximately 2/3 of the total length of the foot (to the back of/widest part of the frog) should be behind the true apex, and approximately 1/3 of the total length of the foot (to breakover) should be in front of the true apex - in the photo there are 3.3 units from purple breakover to brown frog apex, and 6.6 units from brown frog apex to blue back of frog. Red - the true toe runs from the hairline to the ground parallel with the dorsal surface of P3. Inner pink - marks the dorsal surface of P3. Outer pink - suggests the approximate outer edge of the dermal laminae and the true edge of the sole at ground level. As there is almost no sole depth, the edge of the sole is very close to the tip of P3. See how the edge of the sole looks to be much further forwards - what looks like sole in the front of the foot is actually laminar wedge. White - suggests the approximate outer edge of the white line (which is the outer edge of the epidermal laminae), being around 3 mm to the outside of the true edge of the sole. Again, see how it looks as if the white line is just behind the toe on the photo, where you would expect it. What looks like the white line on the sole view is the end of the epidermal laminae, which have been pushed away from the dermal laminae and the gap between filled with laminar wedge - you can see this in the dissection photo above (and see also the diagram of the laminitic foot in the previous images). The true white line will always be just outside the true edge of the sole, growing down from the terminal papillae where the dermal laminae reach the bottom of P3. Purple - suggests a breakover bevel to reduce separating forces on the toe. Ideally this will start at or just to the outside of the edge of the true white line, so 3 to 5 mm outside of the true edge of the sole. Yes, this is very close to the tip of P3 - but that's because there's no sole depth. All of these diagrams suggest an accurate - and therefore quite scary and severe - trim, because of the lack of sole depth bringing the trim so close to the tip of P3. It's great for a model. In reality it always pays to err on the side of caution, but keep in mind that not doing enough can be (almost) as bad as doing too much. In reality, based on the foot shown in the top x-ray (showing the corium in thick pink) you might aim to get the true toe (the red line) rasped in the first trim - as long as the laminar wedge was stable - then put a very small (but steep) breakover bevel behind the true toe, to reduce the separating forces on the toe. Then in around 1-2 weeks, assuming that the bottom of the foot had been rasped into 2 clear planes at the first trim and the horse was now able to weight the back of the foot and relieve the front of the foot and sole, you would expect there to be a reasonable increase in sole depth in the front of the foot, and you might then take the breakover bevel back to or just outside of the edge of the true white line. The angle of the bevel is important - even a bevel just behind the true toe line, if set at a steep angle*, should help to reduce separating forces on the toe (and therefore pain and the risk of further damage). (* aim for a bevel of around 60 degrees in the initial stages of rehabilitation, reducing to around 45 degrees as the foot improves, then finally to 30-45 degrees on the recovered foot). Further information
For members of the ECIR group: Backing up the Toe - Eleanor Kellon August 2017 Toe Rocker - www.all-natural-horse-care.com Laminitis And The Laminar Wedge: Take It Or Leave It Using the Rasp (using and applying the bevel)
Following laminitis, the feet should be supported through the full solar surface, not just through the frog.
1. When frog support only is used on a laminitic foot, the pedal bone is left unsupported with the potential for (further) rotation, sinking and penetration (the example shows a foot with dorsal and palmar rotation): 
The laminae are not properly connected after laminitis. The force of the horse's weight acts downwards on the pedal bone (P3) (blue arrow). A frog support is supposed to support the back of the foot, but the back of the foot is not affected by laminitis and should already be well supported by the horse's own frog. Fitting a frog support potentially lifts the front of the foot off the ground, giving the tip of P3 a hole to fall down into.
On conforming bedding the front of the foot will be supported so the risks of fitting a frog support should be minimized, but the frog support is unlikely to provide any better support than the bedding alone (and may lead to thrush, excess pressure and atrophy of the frog). The dorsal and palmar rotation should be corrected immediately. The purple dotted line shows the breakover bevel back to the outer edge of the true white line. The heel/bottom of the foot trim to return the palmar angle to 3 to 5 degrees is not shown, but see below *.
2. When full solar surface support is used on a laminitic foot, the pedal bone is supported and the potential for (further) rotation, sinking and penetration is minimized:
The laminae are not properly connected after laminitis. The force of the horse's weight acts downwards on the pedal bone (P3) (blue arrow). The foot in front of the true white line is not stable and should not bear weight - the dotted purple line shows the breakover bevel needed to bring breakover back to the outer edge of the true white line, to more stable foot. With full solar surface support fitted, the pedal bone is fully supported, and the ground reaction force acting through the solar support (green arrows) can oppose the horse's weight (dark blue arrow) and any further displacement of the pedal bone (turquoise arrow) - the pedal bone has increased stability. See image below for how the realigned foot would look with full solar surface support.
Conforming bedding may support the foot adequately and whilst a laminitic horse is on wall to wall deep conforming bedding, extra support may not be needed, but if a horse is not fully comfortable, padding the full solar surface should be tried and the horse assessed to find optimum comfort. As above, the dorsal and palmar rotation should be corrected immediately.
3. When the heels are high (i.e. there is palmar rotation), extra support may be needed beneath the frog so that the frog shares weight bearing with the rest of the solar surface, while waiting for realigning trimming to lower the heels and return the palmar angle to normal. However, there should be frog support PLUS full solar surface support (both supports will usually be made from the same material, e.g. EVA foam), and never frog support alone for the reasons given above.
Raul Bras, in his chapter on Solear Support Techniques (in Equine Laminitis edited by Belknap, Wiley, 2017) says that over the last 25 years it has become routine for acute laminitis cases to have the sole and bars as well as the frog supported with pliable material. He states that it is likely that applying supportive material to the whole solar surface of the foot will provide support to the pedal bone (P3), but that using frog support has not been proven to greatly improve support of the pedal bone, and therefore it may be more effective to provide support to the entire sole and the entire solar surface of the pedal bone. Supportive materials used should be similar in hardness/firmness to the horse's frog, and include EVA foam, closed-cell foam and impression material. Discussing frog supports, he warns of pressure around the coronary band from fixings used, suggests that they frequently move out of place, and cautions that no research supports their use. He concludes "it is likely that the greater surface area of the sole addressed by the sole support (especially the dorsal aspect of the sole), the more support will be provided to the DP" (distal phalanx/P3).
It is very important that sole support does not adversely affect the already compromised foot, and thought should be given to the material and design used and to ensure that pressure is released during hoof flight. Dr Taylor (see below) suggests using a shallow air space beneath the margin of the pedal bone when the sole is very thin or perforated. However, if used both the position of the air space and the horse's comfort must be checked regularly, as we have seen the use of an air hole allow the pedal bone to penetrate the sole in a foot that hadn't been correctly realigned.
Jonathon Merritt, Helen Davies and Andrew Parks say, in their chapter on the Digital Biomechanics Relevant to Laminitis (in Equine Laminitis edited by Belknap, Wiley, 2017) that the pedal bone may be supported from below by forces transmitted from the solar surface of the hoof, and that "increasing support from the sole may assist in reducing the force on the lamellar junction." In 2014 Dr Debra Taylor published a paper describing the laminitis rehabilitation protocol that returned 14 out of 14 horses, many with significant rotation and sinking, to their pre-laminitis level of comfort. The hoof care method used the full solar surface to support the pedal bone (P3), protecting the sole during weight bearing by using foam rubber pads and/or dental impression material inside hoof boots (or casts). See Section 2.3: Taylor D, Sperandeo A, Schumacher J, Passler T, Wooldridge A, Bell R, Cooner A, Guidry L, Matz-Creel H, Ramey I, Ramey P Clinical Outcome of 14 Obese, Laminitic Horses Managed with the Same Rehabilitation Protocol Journal of Equine Veterinary Science Volume 34, Issue 4, Pages 556–564, April 2014 (online 05 Feb 2014) See also: Solar penetration Robert Bowker Hoof Anatomy Videos
* The realigning trim restores the palmar angle to 3 to 5 degrees (by lowering the heels gradually) and returns the wall at the toe to being parallel to the dorsal surface of P3 (by following the correct new wall growth beneath the coronary band).
See Recognizing and Treating Rotated Hoof Capsules - Pete Ramey Realigning Trim
Professor Robert Bowker talks about the horse's foot and his physiological trim. Videos first appeared and can be seen on Epona TV.
Edited April 2020 to add Dr Robert Bowker talks to Wendy Murdoch of Sure Foot Equine Stability Program April 2020 (parts 1 and 2).
Hoof Anatomy with Professor Robert Bowker - Part 1 The digital cushion - EponaTV
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The digital cushion is a natural shock-absorption mechanism, which, when well developed, consists of strong ligaments that have adapted into fibrocartilage. Myxoid tissue is a primitive connective tissue (similar to stem cells) that can adapt and respond to whatever is needed if it is stimulated correctly. It is important for the formation of fibrocartilage from fibrous tissue, especially for the frog. Digital cartilage consists of fat cells, myxoid cells and elastic tissue with a fair number of blood vessels between the ligaments. As the digital cushion develops, ligaments start to thicken and the myxoid tissue contributes to fibrocartilage. In a well developed foot, these ligaments run under the DDFT connecting the lateral cartilages, like a trampoline. Fibrocartilage is tissue that is halfway between cartilage and fibrous tissue; it develops or adapts in response to stimulation of the foot under compression/strain. Under compression or strain the fibrous tissue tries to protect itself by producing fibrocartilage – this is a normal adaptive response, not a pathology. In 1941 the Germans had discovered the ligaments in the foot, but not the blood vessels. People have claimed there are scant numbers of blood vessels between these ligaments but there are in fact a fair number of blood vessels. When the foot is on the ground, the ligaments become taut and the volume of the frog increases (causing negative pressure) – RB believes that this causes much of the blood in the foot to be directed into the vessels in between the ligaments, causing it to start to swell (like erectile tissue) and thereby supporting the navicular bone and the DDFT. In a good foot the navicular bone sits on a cushion of thickened ligaments and blood vessels.
Hoof Anatomy with Professor Robert Bowker - Part 2 Navicular syndrome - EponaTV
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Dissections of horses with navicular syndrome (NS) show a lack of ligaments and fibrocartilage or damage to ligaments in the digital cushion, damage to blood vessels and pathologic DDFT tissue. They have less of a cushion for the navicular bone. In comparison, a “good” foot has robust ligaments and a developed digital cushion beneath the navicular bone - “like a training shoe”. When a foot with NS is loaded: 1. it can't support the navicular bone/weight because it doesn't have strong enough ligaments and vessels (due to damage), and 2. the vibrations can't escape the foot, setting up a continuous vicious cycle. In a “good” foot, the lateral cartilages added together usually make up 25-37% of the total width of the foot, and the blood vessels are inside of the cartilage itself. When the vessels are inside the cartilage, when the foot hits the ground, the vibration shock wave goes up through the heels and the vibration is transmitted through the lateral cartilage and can get into the blood vessels to be transported out of the foot. In a foot with NS the total thickness of the lateral cartilages is less than 10% of the width of the foot, and the blood vessels are on the inside of the lateral cartilage. When there’s no support for the navicular bone: the navicular bone starts to move on P3 and starts to sink towards the ground, and the blood vessels are damaged – the vessels not only provide support for the navicular bone but they also nourish the DDFT and other ligaments. Pathology of navicular syndrome shows that it occurs outside of the navicular bone itself & beyond the pressure of the DDFT against the navicular bone. Navicular is an entire foot problem - it doesn't just affect the navicular bone.
Hoof Anatomy with Professor Robert Bowker - Part 3 Peripheral loading: possible but not ideal - EponaTV
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The frog should not be trimmed (between the collateral grooves and the tip of the frog apex), it should be swollen, large and on the ground/weight bearing. When the foot is trimmed to remove the bars so that they are no longer weight bearing, peripheral loading of the walls is increased. The hoof should support the thickest part of P3 through the collateral groove/bar area. When shod, the load of the foot is distributed around the shoe. The rim of P3 is the thinnest part of the bone. When the foot is loaded peripherally, the rim of P3 becomes susceptible to problems like pedal osteitis and frequent fracturing of the edge of P3. The centre of P3 is the thickest part – the hoof should support this area, directly under the roof of the collateral groove. By removing frog and bar material, there is no longer support under the centre of P3 so the foot has to be supported another way. When the foot is loaded peripherally – on the hoof wall – all of the horse’s weight is on the hoof wall. P3 is being suspended from the laminae/hoof wall. RB believes that the hoof wall should support only 5-20% of the horse’s weight, the other 80-95% should be supported by the solar structures, i.e. the frog, sole, bars and dirt plugging the collateral grooves and sole which will support the centre of P3. “The coffin bone really shouldn’t be suspended from the hoof wall by 100% of the weight.” People think the horse’s weight should be suspended from the hoof wall because when a horse develops laminitis, the laminae can no longer support the horse and it appears that P3 comes through the bottom of the horse’s sole - but actually the hoof is moving up the leg. There is a large surface area of laminae, and if the foot is trimmed so that the hoof wall is below P3 (the sole), P3 IS suspended by the hoof wall. But if the foot is trimmed so that there’s minimal weight load on the hoof wall, P3 is not suspended by the laminae/hoof wall, and most of the weight will be on the solar surface of the foot. RB has seen a lot of pathology in horses’ feet where the hoof wall is the loading structure and P3 is suspended from the hoof wall – the foot adapts to try to minimise stress on the connective tissue. In other mammalian species, e.g. ruminants, camelids, the nail (hoof wall) is not the primary loading structure – they walk on some sort of solar pad. The horse has a more keratinised solar pad and a very large digital cushion which contains a lot of ligaments and blood vessels – when the foot is loaded, the blood vessels become engorged and remove the energy/vibration of impact. You should be able to pass a ruler under the hoof wall all the way around – the weight should be on the solar part of the foot. PR made foot imprints as horses left an arena, cleaned the dirt plug out, and the area where the foot was loaded on the arena was inside of the hoof wall. It is thought that P3 doesn’t have a periosteum. This depends on how the foot is loaded. If loaded from the hoof wall the connective tissue overlying P3 (the periosteum) changes orientation so that it is no longer parallel to P3. When the solar surface is loaded, the periosteum is present. RB believes that P3 wants the majority of its weight to be loaded (supported) from the solar ground surface rather than the hoof wall.
Hoof Anatomy with Professor Robert Bowker - Part 4 Stimulating the foot - EponaTV
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Using Dopler ultrasound, able to show that perfusion of the foot changes with the surface the horse is standing on. On a hard surface the same amount of blood is going to the foot, but it stays in the larger vessels. On a conforming surface, small blood vessels become perfused which leads to greater blood flow through the entire dermis of the foot and the internal parts of the foot. Softer conforming surfaces increase perfusion of the foot – studies in humans have found conforming surfaces “more comfortable” and “relaxing”. RB believes the horse may relax psychologically as well as physiologically when standing on a conforming surface. The footing should be firm, e.g. pea gravel or larger gravel. Pasture probably isn’t sufficient for stimulation. In other species on harder (gravel) surfaces bone density increases in the foot and the digital cushion becomes more fibrocartilagenous on pea gravel/gravel rather than pasture. There is no exact distance a horse has to travel – one herd in Canada averaged only 0.5 km/day. Optimal hoof health = the hoof wall bearing only 5 – 20% of the horse’s weight, 80 – 95% of the horse’s weight being born by the solar structures (frog, bars, sole) – this will set up a decent foot. It’s not about distance travelled, but ground contact, suface, degree of hardness are all components of the whole formula
Hoof Anatomy with Professor Robert Bowker - Part 5 Trimming the feet - EponaTV
NOTES
The digital cushion contains tiny blood vessels which make up a kind of hydraulic shock absorption mechanism. General recipe for trimming: Take a marker pen and mark outside the white line. Trim the hoof wall at 45’ to this line. You should be left with the pen line, the white line, sole, frog and bars. Over 100 years ago it was advocated not to touch the sole, frog, bars under any condition. Feet are very adaptable, the foot will adapt to the environment. Keep the toe short, bevel walls, lower heels to the level of the frog. Foot should be 2/3 frog, 1/3 in front of frog. Farrier shouldn’t touch the bottom part of the foot at all. Why do horses become sore when shoes are removed? Shoes make the foot less sensitive to the ground. When the shoe is removed, the foot is much more sensitive to the ground surface – this sensitivity isn’t necessarily pain. It should take a few days, no more than a week, to accommodate. When the shoe is removed, don’t trim the foot apart from rasping the peripheral parts, and see what happens. If sore for more than 4 – 7 days, look for bacterial/fungal infections, examine the foot for pathology. Use boots to protect the foot, keep the horse on a conforming surface e.g. sand, pea gravel, deep dirt. Avoid hard surfaces, allow the horse to adapt and see what happens. (NB this may assume a foot with no known pathologies before shoe removal). Horses shouldn’t be sore for months after coming out of shoes. They could be sore because of thin soles, so protect the foot with boots and pads or keep the horse on a conformable surface. If the sole moves when finger pressure is applied in front of the apex of the frog, the sole is thin. There are natural fluctuations in the morphology (shape) of a healthy foot over time, e.g. the thickness of the sole changes particularly with humidity – in dry conditions the sole becomes flatter and firmer. Don’t trim this – this is the hoof protecting itself. In a normal hoof, regularly check the temperature of the dorsal hoof wall. Heat could indicate an abscess. Take the digital pulse – a soft pulse indicates good perfusion of the foot. A bounding pulse suggests more resistance inside the foot and is not good. When you trim feet, the digital pulse should become softer. RB said owners can rasp their horses’ feet in between professional trims. A pretty foot does not equal a healthy foot. A healthy foot has a very dense P3, with lots of robust ligaments – fibre ligaments have changes to fibre- cartilage. There should be lots of blood vessels through the frog and back part of the foot to help remove energy. These tissues develop as a result of stimulating the solar part of the foot. The front part of the frog is crucial – by trimming the frog you decrease the ability of the frog to develop a good internal foot.
Hoof Anatomy with Professor Robert Bowker - Part 6 Osteoporosis of the coffin bone - EponaTV
NOTES
RB sees many P3s with varying degrees of osteoporisis (OP) – bone loss. Toe clips apply pressure and lead to reduced bone density. As do nails. A crena at the front of the foot is normal. Holes in P3 are not normal but are common. Larger holes are vascular channels and normal. The calcium in P3 is replaced every 5 years so the structure can change over a period of time. So an osteoporotic P3 can increase in bone density by loading the foot from the solar surface and with movement. The back part of P3 will also lay down more bone and become more dense.
Hoof Anatomy with Professor Robert Bowker - Part 7 The problem with metal shoes - EponaTV
NOTES
20 – 30 years ago research showed that when a horse is shod and moving on a firm surface, the vibration energy is very high – 2,000 – 3,000 MHz – this is much less if the horse is barefoot. Vibration energy does not attenuate from the distal to the proximal hoof, and it has a deleterious effect on tissues. If vibration energy is greater than 300 – 500 MHz, this causes blood vessels to constrict - 15 seconds of exposure to this level of vibration caused blood vessels to constrict for 3 days - this destroys the tissues inside the foot, e.g. a shod horse trotting on a hard surface e.g. a road. Pads between shoe and foot attenuate vibration to varying degrees. A shoe loads the hoof wall 100%, RB believes most of the horse’s weight should be on the solar surface – a question of biomechanics. The problem with shoes isn’t that they prevent the hoof expanding and contracting, the problem is the vibration. Research in Denmark concluded that shod horses shouldn’t move above a walk on a hard surface. Don’t pick out the feet before riding – the dirt plug increases the weight bearing area and acts as a cushion and support for the solar surface of the foot, removing the dirt plug increases peripheral loading. Won’t horses get problems with e.g. thrush if the feet aren’t cleaned out? Thrush is caused by an opportunistic bacteria – if the hoof is functioning correctly and the back part of the foot is stimulated, thrush is less of a problem.
Article edited April 2020 to add:
Dr Robert Bowker talks to Wendy Murdoch of Sure Foot Equine Stability Program April 2020 - parts 1 and 2.
Can feet return to having no histology showing that they suffered laminitis, once P3 and the hoof capsule are correctly realigned?
Debra Taylor reported that all the horses that their study followed returned to their pre-laminitis level of comfort, but as these horses were still alive, histology was not looked at: Taylor D, Sperandeo A, Schumacher J, Passler T, Wooldridge A, Bell R, Cooner A, Guidry L, Matz-Creel H, Ramey I, Ramey P Clinical Outcome of 14 Obese, Laminitic Horses Managed with the Same Rehabilitation Protocol Journal of Equine Veterinary Science Volume 34, Issue 4, Pages 556–564, April 2014 The Laminitis Laboratory at New Bolton Centre suggest that secondary epidermal lamellae do not return to normal: On 28 August 2017, the Laminitis Laboratory at New Bolton Center Facebook page posted: "SELs increase the surface area of attachment between the distal phalanx and hoof capsule, but are also affected by laminitis and generally fail to regenerate normal architecture once altered by laminitis or trauma/wear-and-tear."
A foot that has had laminitis should soon look like a healthy foot again - the footprint should return to looking like a healthy foot pretty much immediately after laminitis, the walls may take a little longer as new well connected wall grows down from the coronary band. But what does a healthy foot look like? Here are some examples of healthy feet, and also some examples of not so healthy feet:
It's Not All Pathology! - Daisy Bicking February 2022 Photos - wildheartshoofcare.com - some beautifully trimmed feet with before photos and x-rays Help! What does a healthy hoof look like? Yvonne Welz 2006 Healthy Hooves - www.progressivehorse.co.uk Hoof Education - What makes a good hoof? Jenny Edwards - www.all-natural-horse-care.com Rehabilitation Pictures - Pete Ramey www.hoofrehab.com Healthy Hoof - Linda Cowles - www.healthyhoof.com Healthy Hooves - Paige Poss - www.ironfreehoof.com Healthy feet photos and x-rays: The Horse's Hoof Issue 35 Summer 2009 www.thehorseshoof.com p 24 Dr Debra Taylor has described what to look for in a healthy foot: Physical Exam of the Horse Hoof - Erica Larson - www.thehorse.com 2013 Is the Hoof Smart? Adaptability of the Equine Foot - Dr Debra Taylor (video)
It's not just laminitis that can lead to solar penetration - sadly it isn't rare for vital sole material to be removed during trimming - healthy sole should NEVER be removed within 10 mm (ideally 15 mm) of the bottom of the collateral grooves - see Understanding the Horse's Sole (particularly the explanation of the 2 x-rays 2/3 into the article), and Recognizing Coffin Bone Rotation by Pete Ramey.
In his article "Sinking Coffin Bones", Pete Ramey questions the idea that P3 pierces through or penetrates the sole, pointing out that the sole grows from the bottom of P3, i.e. it is connected to the bone. He suggests that instead of believing that P3 has penetrated the sole, we should ask why the sole is missing - "did the corium abscess and allow the sole to fall off? Did someone cut it off? Did it wear away? Has it failed to grow?".
Prevention
Every step should be taken to prevent solar penetration. On page 351 of Care and Rehabilitation of the Equine Foot, Pete Ramey says "At the first signs of laminitis, restore P3 to a more natural ground plane, relieve pressure on the walls, and pad the sole with foam rubber – vertical sinking and destructive pressure to the solar corium can be prevented”....."Do not wait. Immediate action to eliminate constant pressure on the solar corium and separational forces on the laminae and the coronary papillae can be more important than anything else you do." See Sole Support and EVA foam pads for suggestions for padding the soles.
Trimming
Trimming the foot with P3 penetration of the sole is not particularly different to trimming any foot with rotation:
See Laminitis and the Feet and Recognizing Coffin Bone Rotation. Well marked lateral radiographs should always be taken to guide the trim, but if not available, as the sole grows from and is an extension of the bottom of P3, everything behind the exposed P3 is likely to be sole, and everything in front is likely to be laminar wedge/toe. Collateral groove depths should guide the trim.
Treatment
Horses with solar penetration will usually require soaks and/or poulticing and/or topical applications to prevent or treat infection in the foot, and the feet may need to be kept covered. Baby nappies (diapers) can be useful for draining exudate away from the foot and providing cushioning. Several professionals report good results from soaking solar penetrations with CleanTrax (available from Equine Podiatry Supplies in the UK). CleanTrax contains a proprietary hypochlorous compound which is non-necrotizing and has no adverse effects on normal, healthy cells but eliminates infection from bacteria, fungi and spores. CleanTrax is used on humans to treat deep-seated nail infections and on open wounds/surgeries to eliminate the risk of secondary infections. Other treatments suitable for sub-solar abscesses should be suitable for treating P3 penetrations, such as White Lightning, 50% apple cider vinegar:50% water, warm water and Epsom salts (magnesium sulphate) - see Abscesses. 5 of the 14 horses in Dr Debra Taylor's published rehabilitation protocol had solar necrosis/prolapsed solar coriums (all of the horses recovered). Their soles were treated with topical tetracycline and/or metronidazole. During periods of active abscess formation and/or drainage of exudates from the sole, owners were advised to soak the feet 3 to 5 times weekly in either magnesium sulfate solution or 50% acetic acid solution (TLS comment: we suspect this means 50% apple cider vinegar:50% water solution). See: 2.6. Management Protocol: Medication Taylor D, Sperandeo A, Schumacher J, Passler T, Wooldridge A, Bell R, Cooner A, Guidry L, Matz-Creel H, Ramey I, Ramey P Clinical Outcome of 14 Obese, Laminitic Horses Managed with the Same Rehabilitation Protocol Journal of Equine Veterinary Science Volume 34, Issue 4, Pages 556–564, April 2014 With every case of laminitis, it is essential that the cause has been correctly identified and removed/treated, as well as that the feet are correctly realigned and supported. See Laminitis, EMS or PPID - start here. For help and support, join Friends of The Laminitis Site.
Success stories
Raffi had endocrinopathic laminitis and her pedal bones were threatening to penetrate her soles.
"Trim was applied to realign the hoof capsule and internal structures using Soft Ride Boots. Her feet were soaked in Clean Trax and wrapped in diapers inside the boots until risk of sole penetration and infection was minimal. Then glue/composite shoes were applied. Exercise: Turnout in dry lot paddock with continual access to deeply bedded stall, no forced movement."
2 cases presented to Dr Debra Taylor of Auburn University with perforations in the sole at the tip of P3. Source: Auburn Case Work/Documentation- Ivy and Pete Ramey update 3-14-09 For treatment details see: Clinical Outcome of 14 Obese, Laminitic Horses Managed with the Same Rehabilitation Protocol
Whisky had pedal bone penetration on all 4 feet. He was sent to Andrew Bowe at Mayfield where he was trimmed weekly ("heels lowered to get frogs weight bearing and hoof wall totally relieved from any weight bearing responsibility"), his open wounds soaked daily and poulticed when necessary.
Andrew Bowe - www.barehoofcare.com 
Blossom, a Clydesdale, had pedal bone penetration. She was sent to Andrew Bowe at Mayfield where her feet were trimmed to remove the walls from weightbearing, had daily saline soaks and were protected with nappies and padded hoof boots. She returned to being ridden.
Andrew Bowe - www.barehoofcare.com 
Zara had pedal bone penetration on 3 feet. Her feet were trimmed, cleaned, disinfected and dressed and supported in hoof boots, before she was sent to Mayfield for rehabilitation. 9 months later she was returning to work and galloping in her paddock without pain.
Sarah Kuyken - www.iskanderrun.com.au 
Glynn had pedal bone penetration on all 4 feet. His feet were trimmed regularly (initially every week) and padded and bandaged.
Cynthia Cooper - www.naturalhorseworld.com 
Druid had pedal bone penetration on all 4 feet, with sinking at the coronary bands and abscessing.
Paige Poss - www.ironfreehoof.com 
Monroe, a pregnant sports horse broodmare, had pedal bone penetration on both front feet following an infection.
More information
Reading Sole Thickness - Pete Ramey Horseback Magazine June 2013 Why Does My Horse Have a Thin Sole? - Pete Ramey Horseback Magazine July 2013 Understanding the Horse's Sole - Pete Ramey Clinical Outcome of 14 Obese, Laminitic Horses Managed with the Same Rehabilitation Protocol |
Healthy v laminitic foot Deep digital flexor tenotomy following laminitis Laminitis rehab - barefoot v shod Hoof sloughing The realigning trim - the front of the foot Sole support v frog support Robert Bowker Hoof Anatomy videos Can feet recover fully after laminitis? What do healthy feet look like? Solar penetration Trimming overgrown feet- Aladdin's slippers Are rubber mats better than concrete beneath bedding? Archives
July 2021
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