05/13/2026
The Hard Sole Plane - great post from Jaime Jackson for the Isnhcp - Institute for the Study of Natural Horse Care Practices
Hard Sole Plane – Praetorian Guard of the Sensitive Sole
I have been asked to clarify the meaning of the term Hard Sole Plane (HSP) as I understand and define it. At its root meaning, it is a barrier established by the laws of nature not to be crossed in hoof care. It is codified in the Four Guiding Principles of the Natural Trim derived from the wild horse model:
1. Do not remove that which nature intends to be there.
2. Remove only that which naturally wears away in the wild.
3. Allow to grow back that which resulted from human meddling.
4. Ignore all pathology and simply do the right thing and nature will heal.
These pillars are all also deeply ensconced in the premise of “do no harm” and “respect the healing powers of nature” from the Hippocratic Oath. It is a sacred oath to be upheld by students of the ISNHCP training program and our qualified NHC Practitioners. Crossing the HSP with willful intent is an egregious violation of the Oath and has been grounds for removal from both the AANHCP and ISNHCP more than once.
Understanding the HSP is not simply an academic quest; it must also be taught and verified in a clinic environment with cadavers before taken to the living hoof. Typically, several years of training are needed.
Technically, the HSP represents the surface of the sole that faces the environment. Its counterpart is the Live Sole Plane (LSP)—the growth corium where the epidermal sole is created. It is a highly sensitive and vascular area of the hoof. The HSP is divided from the LSP by approximately 1 cm of epidermal sole, seldom less and commonly not much more. The quality of the sole in between the HSP and LSP is as important as its thickness. For example, Whole Horse Inflammatory Disease (WHID) degrades the natural integrity of the sole: It becomes sick, weak, and spongy in places, particularly around and forward of the point of frog. But so do trimming methods that repeatedly crossover into and even through the HSP. Hoof knives are kept razor sharp to filet through the resistant sole. In time, failed efforts by the LSP to counter these intrusions result in hypersensitivity, paper thinned bleeding soles, hoof contraction, splayed hoof walls, and epidermal scar tissue, particularly when the bars are also scooped out. I am talking about ruined hooves. Such hooves (as cadavers) commonly came through my training clinics dating to the earliest days of the AANHCP and ISNHCP. It continues to be a significant problem to this day.
Intrusions of the HSP are often targeted, and reflect different methods and strategies. Collectively, no part of the greater sole is spared. Some target the heel buttress and their seats of corn by flattening the heels with the flat rasp; others carve out the sole across the toe until they are bleeding, then cauterized; others “gouge” the entire sole into a bowl. Some have gone so far as to drill holes through the HSP and into the LSP; in one case on a living horse I was asked to investigate had five drilled holes on both front hooves. The purported rationales made no sense and I won’t mention them here. There are many more examples of this I could provide, these immediately were off the top of my head. Such hooves do not arrive at the abattoir with happy horses attached to them.
The HSP in the Natural Trim is approached through an evaluation of solar plates through nipper dragging and measuring toe length (HTL), and toe angle (H). These steps alone are enough to determine if there is excess sole or not. I also tap the solar dome to listen to its audible vibrational response, which can signal sole quality and density. If severe sole compaction is determined by the previous steps, it is opened up by initiating what are called “clean cuts” with the hoof nippers applied at strategic points along the hoof wall from toe to bar. The sole is not touched beyond the preceding minor nipper dragging. This induces a reaction in the papillary bed of the hoof wall’s coronary corium to release solar plates bound within its walls. The sole corium initiates a secondary release response to dump its waste. The horse is then set out to move freely on track with dry footing, preferably with sufficient hard standing to expedite the exfoliation. The horse is then revisited in several weeks to continue the nipper dragging, wall removal, and critical measurements. Most of the time all releasable solar plates are taken with the dragging, exposing the HSP. A sole rasp or sand paper can be used to remove residual loose solar plates or ignored. Regular Natural Trims will be necessary to maintain the HSP with minimal or no solar waste.
Horses in my care at the AANHCP Paddock Paradises never saw a hoof knife applied to their soles or frogs in the eight years we were there. HTL and H were steady in the measurement ranges of the Hoof Meter Reader (HMR). In terms of trim mechanics, this was made possible by the Natural Trim method and strict adherence to its Four Guiding Principles. Again, this must be taught in a clinic environment, as there is much nuance that escapes the pages of any academic text on the subject.
J. Jackson
for the ISNHCP
