Well, it seems there is some controversy mulling about on social media about the Digital Cushion of the horse's hoof and if can be rehabilitated once its been corrupted by any means.
Some want scientific studies while others are content with evidence based findings.
From a professional hoofcare standpoint I can only state, unequivocally, findings that I've personally seen and to which I've tended.
I'll say this ... the horse doesn't lie. And my answer to whether or not the DCs of a horse's hoof can be regenerated to a healthy state is ... absolutely.
Hoof on left with poor DC; hoof on right with well developed DC. Hoof on left in beginning stages of rehab; hoof on right maintained in healthy state.
Can I say with 150% surety? Nope. But I can tell you that all I worked on, except for one that was sold and I lost connection with him, went back into work and did so soundly. 100% sound. THAT tells me that the DC was restored. Why does that tell me ?
If the horse is sore he tells us. He doesn't pretend to be sound when his feet hurt. Corrupted digital cushions cause pain in the rear of the hoof - most commonly labeled as "Navicular" as each step exerts thousands of psi upon the loading of each hoof.
I prefer the label of "Caudal Heel Pain" (unless, of course, it has been determined that Navicular DISEASE is present and not just Navicular "Syndrome")
Let's briefly go over exactly what the Digital Cushion in the horse's foot is.
The Digital Cushion (DC) lies above the frog of the hoof, inside the foot. A healthy DC is comprised primarily of Fibrocartilagenous tissue - that is tissue that is meant to stand a pounding. The layers of fibrocartilageous tissue is lightly interspersed with fat tissue. (take note of the word "lightly", please.)
In a healthy, correctly formed hoof, the DC is going to be robust and provide a great 'trampoline effect' for when the foot is loaded and the P2 is slammed down towards the ground with each loading step. (1)
Now, think of this -- think of what happens when we bite into a piece of cartilage in nice, thick juicy steak or piece of chicken. We chew and chew and chew but cannot bite through it and the cartilage remains intact and goes back into its original shape after each attempted bite.
What happens when we bite into fat? It's soft and easy to chew and break it down to pretty much mush.
The same principle happens in the foot of the equine digit ... a nice, thick, fibrocartilagenous DC is going to give slightly to the 'bite' of hoof loading and rebound nicely in the foot while the DC that is primarily fat is simply going to get squished providing little to no protection for the pounding the P2 gets on hoof loading. It turns to mush. BUT ... with the containment from the lateral cartilages and the frog apex the shape is more or less retained. Perhaps shrunken a bit but still contained somewhat.
"Histological and functional characterizations of the digital cushion in Quarter horses", Babak Faramarzi, Linnea Lantz, Dongbin Lee, and Wael Khamas
Briefly ... and this can be verified by a quick study on the (medical) attributes of fibrocartilagenous tissue and how it repairs ... the more stimulation of the fibrocartilagenous tissue the greater the vascular system in the DC and the more cartilage can develop. The more the hoof receives good stimulation with movement (very basic here), the more the DC develops from the added nutrients and oxygen it receives from increased circulation. For a horse that stands in the stall or in one place much of the day, the more fat develops in the DC than fibrocartilagenous tissues. Thus the shock absorption of the DC is diminished greatly.
To further the suspension system in the foot, healthy DCs will readily connect with the Lateral Cartilages (LC) to suspend the P3 (Coffin Bone) in a strong, energy dissipating and shock absorbing 'sling' underneath the P3.
The healthy hoof has quite an intricate and amazing suspension system. However, a hoof that is incorrectly trimmed, is not "fed" properly, does not get good stimulation is going to fall prey to the degeneration of healthy fibrocartilagenous tissue to simple fat tissue. Although, various studies will differ on this ...
"There are significant inconsistencies in previous reports describing the composition of the DC. One study stated that the DC is composed of only elastic fibers and adipose tissue (7). Another study examined the histology of the DC and reported that the equine DC consists primarily of tightly packed collagen fibers with only a few interspersed elastic fibers and very little adipose tissue (8). A more recent study indicated that the DC contains connective and adipose tissues, elastic fibers, and tissues with matrix rich in hyaluronic acid (5). Collectively, these studies disagree about the architecture of the DC. Such differences might be due to variability in sectioning techniques and can partially be explained by examining the distinct regions of the DC." Histological and functional characterizations of the digital cushion in Quarter horses", Babak Faramarzi, Linnea Lantz, Dongbin Lee, and Wael Khamas
BUT .. this damage can be reversed. To what extent, I don't know but, suffice to say, the horse will let you know. Again, the horse does not lie. It is either sound as a dollar and happy to travel over any terrain or the horse is not sound and presents as tender and sensitive on hard ground or rocks.
There might not be many current 'scientific studies' to prove all this but a little bit of knowledge of different tissues and what their function and development entails in the equine hoof and foot will help connect dots so it all just simply make sense.
This regeneration is not something that takes place instantly with just one correct trim but can be quite evident with a full hoof growth cycle of 8 months to a year.
(1) The cartilages of the foot, also referred to as the collateral cartilages of the distal phalanx, ungular (ungual) cartilages, and lateral cartilages, originate as hyaline-type cartilage and become fibrocartilage in adults.1 They attach to the proximal border of the palmar processes of the distal phalanx. The size and shape vary, as does the degree of ossification. The cartilages have axial extensions, and they seem to provide an internal support structure for the palmar (plantar) aspect of the foot.2 An extensive network of venovenous anastomoses is present within the cartilages. Marked differences in the thickness and tissue composition exist in the front and hind feet. The cartilages of the foot tend to be thicker in forelimbs than in hindlimbs, perhaps reflecting the greater weight-bearing capacity of the forelimbs.2 The digital cushion has more fibrous or cartilaginous tissue in forelimbs than in matched hind feet, which have more adipose and elastic tissues. There may also be breed differences. An extensive and complex relationship exists between the cartilages of the foot and the digital cushion. The combined role is thought to be energy dissipation, which depends on hemodynamic flow.2 -- Sue J. Dyson, "Diagnosis and Management of Lamenss in the Horse (Second Edition), 2011
To simplify this and put it all into layman's terms ... as I stated above, "The Digital Cushion (DC) lies above the frog of the hoof and in between the lateral cartilages, inside the foot. A healthy DC is comprised primarily of Fibrocartilagenous tissue - that is tissue that is meant to stand a pounding." Exercise, as indicated by studies, show that immature DC's are primarily made up of fat and mature, healthy DC's are made up primarily of fibrocartilage. The more stimulation that cartilage receives, the more vascular resources develop within the structure -- more blood supply. "Science" tells us good, healthy tissue (most kinds) need nutrients and oxygen for maximum health. So it only stands to reason that the DC's that get most stimulation are going to be consisting mostly of fibrocartilage with a good blood supply interspersed for regeneration and repair when needed.
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Gwen Santagate is the author of "10 Secrets to Healthy Hooves" . For the last 37+ years, she has maintained healthy hooves with natural trimming on thousands of horses and specialized in pathological rehabilitation hoofcare for the last 18 years. She keeps a small herd of her own equines and continues to offer consults for horses in need.