A lot of folks, both farriers and veterinarians, are advocating a system of trimming horses' feet that involves just enough science to sound plausible; however, on closer examination, the methodology requires belief in the horsy equivalent of the Tooth Fairy.  As I understand it, the trim consists of dropping the heels until one has frog pressure, gutting the quarters, boxing the toe, whacking out that portion of the toe that would fall between the toenails of a shoe and using the sole as a primary weight bearing structure.

Basically, the so-called "four point trim" or "natural trim" is a reflection of the wear of horses' feet in abrasive environments, but such wear cannot be demonstrated to be a Good Thing. Trimming a horse a certain way because they will eventually wear their feet in that manner is just as logical as rasping off the rubber on one's tires because that's the way they'll eventually wear.

The weakest points are the quarters, so they wear away first. However, purposely whacking away the quarters in an effort to imitate normal wear is counterproductive because much of the strength of the hoof is derived from its cone-like construction. A cone works better (i.e., has the ability to carry a greater load) when it's ground surface is in one plane. Furthermore, it can be demonstrated in the laboratory that a horse's hoof is better-suited for function (i.e., protection of sensitive structures, support of the horse) when the ground surface is intact.

Regardless of the horses natural phalangeal angulation, the heels are dropped until the frog is in contact with the ground; this, despite the fact that it can be demonstrated that the most efficient phalangeal alignment is in a straight line. (With reference to this procedure in treating navicular syndrome, one fellow calls it an "Act of faith..."; but I think it's more akin to that particular "faith" that is periodically demonstrated by lemmings.)

The toe is shortened as much a practicable and boxed. This represents the only portion of the procedure that is scientifically justifiable because it effectively shortens the phalangeal lever, thereby facilitating breakover and making the beast more efficient at any gait.

As if to atone for doing something that can be shown to be beneficial to the beast, the so-called "natural trim" dictates that the center of  the dorsal/distal portion of the wall be whacked away so the horse bears weight on its sole.

This practice directly contradicts the tenets of O. R. Adams, DVM, MS, Lameness in Horses, the standard lameness text of most veterinary and farriery courses on equine lameness, which states, "The weight bearing structures of the foot are the wall, bars and frog..." A careful reader will note that the sole is conspicuous in its absence.

Every few years, somebody attempts to relate the feet of feral horses to those of domestic horses.

Twenty-five years ago, Jim Miller used data gleaned from feral horses in formulating his theories relating to the mechanical treatment of navicular syndrome by increasing phalangeal angulation and decreasing phalangeal length. He published his findings in Horseshoeing Theory and Hoof Care (co-authored with Leslie Emery and Niles Van Hoosen, DVM) and the information therein remains useful in palliating navicular syndrome.

Unfortunately, the latest jumpers-on of the feral bandwagon have failed to see the forest for the trees. They point out that feral horses have box-like, semi-clubby feet with broken-out quarters and, since it occurs in feral ("wild") horses, they assume this represents "natural" wear and is thusly a Good Thing.

Which is okay, until they attempt to extrapolate that data to domestic horses.

It doesn't work that way. The so-called "four-point trim" is bad science for several reasons. A domestic horse, used under saddle, is required to carry as much as 20% of its body weight on its back. Furthermore, 60% to 65% of that added weight will be carried on the horse's front end; additionally, many domestic horses, both ridden and driven, are required to engage in forced, repetitious exercise.

Since these factors are not considered, observations on the foot wear of feral horses without regard for the relationship of anatomical form to efficient function become meaningless because they cannot be logically applied to domestic horses.

The most important lesson to be learned from feral horses relates directly to efficiency of motion and was noted by Miller, et al. Horses at liberty in abrasive environments invariably wear their hooves in such a manner that it becomes easier for them to turn their foot over. Technically, this wear results in a phalangeal lever that is shortened as much as possible with as much angulation as practicable within normal parameters.

What'n hell's a phalangeal lever? The phalanges are the last three bones in the horse's leg. The phalangeal lever is formed by these structures and their covering, with the ground acting as a fulcrum. The length of the phalangeal lever is measured dorsally, from the fetlock to the breakpoint of the foot; phalangeal angulation is measured by the angle of the aligned phalanges. Both the alignment and angulation must be evaluated radiographically in order to be accurate, however, they can be measured approximately by means of a hoof protractor. Please note that the breakpoint does not necessarily mean the length of the distal/dorsal portion of the hoof capsule and that phalangeal angulation does not imply natural angulation. Both length and angulation can be manipulated to make the the horse more efficient at any gait.

Simply put, if a horse is going from point "A" to point "B", then the horse with short, steep phalangeal levers (within normal parameters) will exert less effort in getting there than will a horse with longer levers. This increased efficiency translates directly into reduced fatigue and, obviously, a reduced rate of fatigue-related injuries.

In my opinion, one can learn a great deal from feral equids in abrasive environments, but what one learns must be evaluated in accord with what one knows about the anatomy and physiology of the equine foot, as well as the physics of efficient motion.