In recent years, there has been an abundance of published information on the length of toe affecting normal function of the horse’s limb. In the November, 1999, issue of American Farriers Journal, “Strategies For Overcoming Long-Toe, Underrun Heel Concerns” concluded that long toes caused low heels.
The May, 2000, issue of The Horse contained an article on the four-point trim, which inferred that long toes cause dished feet.
We must be terribly naive to believe that both of these foot problems, which are extremely different in appearance and hoof mechanics, are caused by excessive toe length.
We’ve been led to believe that “natural” must mean an improvement over past methods of trimming. We’ve also been told that squaring, rocking, rolling or “setting back” the toe improves the horse’s mechanics and hoof function. Easing the breakover must make it easier for the horse to move.
Or does it? What is the difference between the functions of the toe and heels? How do these hoof parts provide different applications of mechanics for the front and hind leg? Do we understand form and function? Maybe not.
Front Vs. Hind Limb Function
The difference between the workload of front and hind limbs is the most confusing concept. Quite simply, the front legs provide the majority of lift for the body (vertical acceleration) and a small percentage of horizontal acceleration, while the hind legs provide the majority of horizontal acceleration and a small amount of lift.
We have heard and read for years that since the center of mass of the horse is behind the front legs, we must provide posterior support for the front limb. This is provided by length of shoe, egg bar shoes, removal of hoof at the heel to locate the buttress of the hoof or heel of the shoe further under the cannon bone.
These treatments are all mechanically good ideas that will support the body during load acceptance (the first part of the weight-bearing phase). They also give support during the lifting of the body in part of the load application (propulsion) phase.
Conversely, the center of mass is in front of the hind limb. During the load acceptance portion of the weightbearing phase, the hoof is in front of the hip and is loading on the posterior side (heels). During the propulsion phase (load application) of weight bearing, the hoof is behind the hip and the toe is loaded.
In the standing horse, this mechanical difference is significant in that if you could saw the horse in half through the center of its mass, the front half would fall backwards and the back half would fall forward. When standing, the weight of the horse is borne on the heels of the front feet and on the toes of the hind feet.
To appreciate the sensation for these mechanics, stand up straight, plant your feet squarely under your body and lean backwards. It’s impossible, because there is no support for your center of mass that’s moving behind your support. If your shoes were lengthened and nailed to your feet, then you could lean backwards.
Stand comfortably again with your toes pointing straight forward, heels on the ground and lean your body forwards. Feel how the stress is applied to the back of your leg.
Lift your heels (your heel is approximating the horse’s hock) off the ground until you feel the weight pass from the back of your leg into the front part and toes of your foot.
This is how a horse stands all the time. The horse’s hind toe provides support for the body mass while standing, just as the heels provide support for the front limbs.
Shoeing Front, Hind Feet
Shortening the heels of the front shoe will not enhance the front leg’s mechanical function and will most likely inhibit it. Logically, setting back or squaring the shoe behind the edge of the foot or otherwise altering the hind foot’s ability to support the body would not promote better mechanical function.
This is true for the horse whether he is standing or propelling himself forward. Systematically squaring, rocking or setting back the hind toes does not allow the horse to apply force to the ground correctly for standing or movement.
Unfortunately, a tremendous number of farriers practice these techniques on the hind feet. Reducing the hind toe’s ability to support the body for standing or horizontal movement requires the front legs to provide more horizontal propulsion than they should.
This additional mechanical load on the front limbs requires the horse to pull himself forward, thus requiring more mechanical exertion by increased force to the ground or increased contact with the ground.
This begins a sequence of events that leads to gait and/or shoeing problems, which will eventually overload the front limbs and may cause lameness.
Toe Length, Sole Type
We must consider the importance of the correct length and fit of the toes. Horses have minimum requirements for hoof base (both toe and heel for support and propulsion), toe length, frog support, toe angle and sole depth. In defining minimum and maximum lengths for any foot, you must consider the wall length required to adequately cup the sole.
This hoof wall length and sole cup relationship provides the support that the internal structures of the hoof require during weight bearing. A flat-soled horse does not have enough wall to cup the sole. The depth of the cupped sole must also be adequate to provide protection from terrain damage to a soft, overtrimmed sole or the coffin bone.
The shape of the cup and length of hoof wall is required for the horse to dig into the ground for horizontal acceleration. A hoof angle that provides hoof and pastern alignment is mandatory, and frog support is necessary for adequate hoof function.
The hoof and shoe base provides support for the bony column and its applied mechanics. The base provides support for the body to accept load or apply load during movement and standing. Failure of the horse to accept a load correctly (for example, rocking back) or apply load properly (slipping) will result in inefficient application of force and movement.
The hoof and shoe base combined with a proper toe length allows the deep digital flexor apparatus to provide the propulsion needed to move the horse’s center of mass. This means that the horse picks up its foot when it is done applying force to the toe.
Premature breakover before the leg has finished applying force to the ground causes excessive shoe wear at the toe. It causes the horse to apply more force to the limb on the next step to maintain acceleration.
Many factors contribute to proper limb function, including toe length, sole cup, sole depth, frog support, adequate heel and toe support correlated with body weight, foot base size, shape and proper positioning under the leg. Systematic removal of toe wall without consideration of hoof and limb mechanics or body mass is not in the horse’s best interest.
Consideration of these mechanics brings us to the conclusion that larger horses with higher work loads require a greater hoof surface area. These horses have greater mass to move and require more traction and surface area to accomplish the mechanical task.
Horses with longer pasterns have a higher load acceptance than a horse of equal weight and shorter pasterns. Therefore, they will need a higher load application (propulsion) to remain in mechanical balance. Any toe modification of the shoe or hoof that reduces these mechanics below the minimum necessary for proper function will make the horse less efficient in force application to the ground, which enables movement.
We have long understood the concept that the heel of the front foot provides limb and body support for weight bearing and load acceptance. As farriers we must understand that the horse’s hoof and limb mechanics provide vertical propulsion through the heels while accomplishing horizontal propulsion with the toes.
Anything less than the most efficient foot possible is unacceptable to the horse and unethical for our shoeing profession.
1. Kane, J.W., Sternheim, M.M. Physics. John Wiley & Sons, Inc., New York, N.Y.: 1978.
2. Luikart, R. In Pursuit Of The Center Of Balance. American Farriers Journal, 1989; 5: 16-20.
3. Luikart, R. Soft Tissue Function During Weight Bearing. Unpublished.
4. Luikart, R. Horseshoeing Red Flags. Unpublished.
5. Redden, R.F. Do’s and Dont’s of the Four Point System. The Horse, 2000: May, 97-106.
6. Rooney, J.R. The Mechanics Of The Horse. Robert Kreiger Publishing Co., Malabar, Fla.: 1980.
7. Snow, V.E., Birdsall, D.P. Specific Parameters Used To Evaluate Hoof Balance And Support. Proceedings of the American Association of Equine Practitioners 1990: 299-311.
8. Turner, T.A. The Use of Hoof Measurements For The Objective Assessment Of Hoof Balance. Presentation to the Bluegrass Laminitis Symposium, 1993. 0101HTML 7/24/15, 2:51 PM file:///Volumes/LM1/0101HTML.html Page 19 of 156
9. Various Authors. Strategies For Overcoming Long-Toe, Underrun Heel Concerns. American Farriers Journal, 1999: 6, 19-33.
Randy Luikart is an American Farrier’s Association Certified Journeyman Farrier and examiner in Mansfield, Ohio.