This is the second part of this horse hoof essay and now it’s time to describe how I recon the horse hoof is built and work, not from an experts point of view I must add, we are still learning.
The horse hoof – design and function
Looking at the horse hoof it is obvious that the walls of the hoof provides a protection for the sensitive internal tissues and they also give an extremely good grip in any terrain. As a solid mechanics engineer I can also conclude that the walls must be a refined elastic structure, an important link in a system of bones, joints, muscles and ligaments that dissipates kinetic energy as the hoof hits the ground.
Fixating the walls with an iron horse shoe takes the walls out of that system, putting more stress on the other parts. Any changes made to the hoof may of course cause an increase of strain on joints, ligaments, and tendons all the way up to the shoulders and the hips. Research at SLU (Swedish Agricultural University) has shown that 65% of the kinetic energy is absorbed in the system between the walls and the coffin bone.
A hoof is an incredible compact system, still it can absorb more energy than the suspension system of an average car. This is how I figure that out;
The amount of kinetic energy a system can absorb is dependent on the mass and the speed of the object and thirdly the time it takes to stop it (which is dependent on the stopping distance). A horse hoof capsule can be compressed about 10mm, while a cars suspension is compressed about 100mm. Lets say a car weighs 3 times as much as a horse and that the horse hoof capsule absorbs 65% of the kinetic energy, while the cars suspension absorbs 100% it results in that the strain on the hoof is 2,18 times the strain on the car suspension, given all other factors equal.
Note that the speed and frequency at which a stampeeding hores hoof hits the hard stony ground is widely more forceful and dynamic than what a cruising family car experiences on a smooth highway. Above all this is not a reason to justify the use of an iron horse shoe, it is a reason to think twice before altering a naturally perfected system.
Contrary to common belief a soft ground puts more total strain on the hoof and lower legs than a hard ground, especially for tendons and ligaments.
The growth of the hoof capsule begins with mitotic activity in its deepest layer into the basal layer. As the cells matures and migrates slowly outward towards the surface proteins accumulate into their cytoplasm causing the cells to die and dry up into microscopic layers of keratin.
The average mature hoof grows 6 to 9 mm per month, which means that a new hoof grows out during a year. The hooves of foals and yearlings grow 12-15mm per month. When a foal is young the hind hooves grow 12% faster than the front hooves, but by a year’s age there is no difference. Hooves grow faster in spring and slower in winter. Injury or infection in the hooves can cause rapid growth.
It is believed that hoof quality is improved by proper balanced nutrition, still the best hooves grow on wild North Dakota prairie grass, not on neatly packed industrially produced and scientifically developed “Special Performance Horse Mix”.
The walls of the hoof capsule are composed of three layers that grow downwards together. The pigmented layer is a hard protective surface and often breaks away in flakes at the bottom. The water line has a structural function, highly resistant to wear and its thickness increases towards the ground. The white line is the light softer inner layer of the wall.
Because the wear of the hoof varies by the amount of movement and the nature of the terrain the walls will sometimes stick out from the sole in lack of sufficient wear, then a barefoot horse hoof will self trim by chipping off at the rim. The walls of a shod horse do not wear at all, so naturally they must be trimmed regularly.
The frog is a relatively hard rubber-like frog-shaped feature under the hoof that serves as a shock absorber and provides a good grip on slippery smooth surfaces, but most importantly it works as a pump, it actually pumps blood from the hoof back to the hearth!
It’s good if the frog gets to wear and harden properly against the ground. If horses that stand inactivated in stables on urine acid impregnated bedding the frog may get infected and break down to a soft sore surface and totally loose its important functions.
The more or less white sole covers underside of the hoof, except for the frog. The bright smooth surface has a hard consistency. In shod hooves the sole may get brittle in lack of ground contact and the surface may rub off when scratching with a hoof pick.
The bars are the parts of the walls that folds inward towards the frog at the heel at a sharp angle. The part of the sole that’s between the walls and the bars is called the seat of the corn. If the bars do not wear enough they bend towards the sole.
The lowest bone inside the hoof has many names; the coffin bone, pedal bone or third phalanx (P3). It is covered by the hoof capsule and has a cup like shape that resembles the walls. Between the wall and the coffin bone is the corium which is the glue that connects the wall to the coffin bone, it’s called the laminae. Closest to the coffin bone is the sensitive laminar layer with nerves and blood supply. The inner wall has a similar, but insensitive, laminar layer that fits, and is strongly attached, to the coffin bones laminar layer. Inflammation such as laminitis can cause the hoof wall to pull away from the coffin bone.
Over the rear part of the sole is the digital cushion, protecting the internal structures working like a shock absorber.
A foal has in general terms identical front and hind hooves, but as the horse matures they change shape and adapts to the variation in its use and the horse’s movement patterns.
The hoof is a flexible system that changes shape as it is loaded. When a hoof touches the ground there is only contact at the heel and at the toe, as pressure is applied the lower wall edge, the sole, the bars and frog gets engaged, the plantar arch flattens, solar concavity decreases and heels spread, the hoof diameter increases, the coffin bone presses towards the hoof capsule. Blood pours into the corium and when the hoof is unloaded the hoof restores its shape and blood is squeezed up and as the flexion of the foot raises the blood pumps further up in the blood vessels giving life to the hoof system.
It’s not very difficult to imagine that a fixed iron shoe will affect a refined system like this. Medieval ignorance may be forgiven, but what are the excuses in the 21st century? The next part will deal with the horse shoes, so stay tuned.