If, according to an old English proverb, the eyes are the windows to the soul, then for horses and humans the nails and hooves may well be the windows to inner health or medical problems.
Careful and close attention to the exterior hoof capsule and related anatomical structures often can provide a wealth of information concerning environmental factors, nutrition, infectious diseases, toxicities, deficiencies and farrier care.
In their 1999 Manual of Equine Dermatology, Dr. R.Pascoe and D. Knottenbelt address this in the section on hoof problems. "Inevitably some disorders of the hoof have profound implications for the welfare and health of the animal itself," the doctors write.
"The hoof offers (the clinician) clues that are not present elsewhere," he says, "yet the rigid hoof capsule inhibits basic palpation of the structures within the foot." And the usually pigmented surface does not allow veterinarians access to as much information as can be obtained from human nails. "Therefore," Parks advises, "it is important to develop an ability to 'read' the hoof capsule (which seems to be a life-long process)."
Clinicians should have a good understanding of the structure and function of the hoof capsule and use abnormalities in growth and appearance to gain possible insight into systemic conditions and diseases. The hoof is simply too good a "window" not to utilize the view.
Composition and pigment
The hoof is a modified cornified epithelium, and is approximately 25 percent water. It is composed of three layers.
The third, or inner, layer is the laminar layer that forms the epidermal connection to the dermal laminae below. Blood is supplied to these various layers by corresponding layers of modified vascular tissue. The periopic corium, coronary corium and laminar corium provide nutrition and vascular support to the hoof wall.
The generally accepted rate of hoof growth is 1 cm monthly for a healthy horse in a moderate environment receiving good nutrition. Deviations or extremes in numerous factors can seriously affect hoof growth and its ability to heal and regenerate.
Examining the hoof
Additionally, it should be evaluated in its relationship to the column of the leg by sighting down the carpas-cannon line when viewing from above. Imbalance or abnormalities in confirmation, such as off-set hooves (medially or laterally in relation to the position of the cannon), low heel height, upright phalangeal angles or other variations can result in imbalanced landing and loading forces that can shift and alter the growth and appearance of the hoof.
It is then important to determine if these changes are the result of genetic variations in the bony structure of the horse, to inconsistencies and irregularities in farrier care or to a combination of both.
Radiographs often are essential in determining just how a particular horse should land and load weight on its hooves and how best to trim and/or shoe that horse to maximize this correct motion.
Horses with brittle, uneven hooves, imbalanced growth rings or various types of hoof cracks may all be suffering from some form of mechanical imbalance. Horses that do not hold shoes, that tend to break off sections of hoof, that either do not grow foot or tend to wear off hoof unevenly, may all be in this imbalanced cate-gory as well.
Good farrier attention aided by radio-graphs is the best solution for these cases, and it must be stressed to clients that this is a long-term process and will require a number of trimmings to achieve.
It has long been accepted that the horse needs, along with good baseline nutrition, adequate protein, biotin, calcium, magnesium, methionine, zinc, sulphur, choline and copper to produce optimum hoof.
The hoof is composed largely of protein, and horses with low protein levels in their diets will have brittle, thin hair and weak, slowly growing hooves.
Fortunately, most commercial diets and most good pasture environments provide adequate protein to healthy horses.
Numerous studies have shown that biotin supplementation increases the growth rate and the eventual hardness of horse hoof. Scanning electron microscopic images taken of hoof horn from horses with brittle feet revealed that biotin was not the entire story, however.
Dr. S. Kempson of the Royal (Dick) School of Veterinary Studies at the University of Edinburgh showed that two types of defects were observed in horses with brittle feet. The first showed a loss of structure and horn, which was remedied with biotin supplementation. The second showed poor attachment of the horn to underlying structures, which was not reversed with biotin supplementation and required calcium supplementation as well. Therefore, adequate calcium and biotin are both necessary.
Magnesium is closely associated with calcium metabolism, and low magnesium levels have been associated with some types of laminitis, so levels of this mineral nutrient should also be monitored.
Sulphur is important in hoof growth and is incorporated into specific amino acids such as methionine and cysteine. Zinc and copper also are needed for hoof growth and the interrelationships between all of these nutritional factors quickly become crucial.
Deficiencies of any of them will inhibit proper hoof growth, but excesses can be just as detrimental. Excess calcium inhibits the bioavailability of zinc. Excess methionine decreases the absorption of copper and zinc. Overall it is essential that a good balanced diet with appropriate levels of crucial horn growth nutrients is available for all horses that exhibit problems with their hooves.
Diseases and infection
Infectious and systemic diseases can cause changes in the equine hoof. Various bacterial and fungal organisms can attack the skin at the coronary band and cause inflammation, irritation and sections of scabs and crusts.
Lymphangitis (of bacterial, viral or toxic nature) can cause excessive swelling along the coronet leading to serum extravasation, lipping of the coronet over the hoof capsule and even to hoof separation.
Autoimmune skin diseases such as Pemphigus foliaceus can cause hair loss and swelling at the coronary bands with associated lameness. These cases can progress to bullous-type lesions along the coronet. Vesicular stomatitis, foot-and-mouth disease and other viral infections also can affect the coronary bands of horses, and clinicians should be ever vigilant for these unique but very serious problems.
Often a mild lameness and inflammation of the coronary bands are the first lesions seen, and an observant practitioner will spot these signs and recognize that hoof abnormalities often reflect systemic diseases.
Toxins can cause problems with hoof growth as well. Selenium toxi-city will cause horizontal ridges in the hoof wall along with cracking and even sloughing or separation along the coronet.
Many poisonous plants, such as milk vetch, woody asters and golden weed, can cause inflammation and possible instability of the coronet.
Chronic diseases in other organ systems may influence absorption and digestion of needed nutrients, blood flow and distribution of those nutrients and general hoof growth.
As early as 400 B.C., Hippocrates taught that nails reflected the inner body. Abnormalities of the nails, he believed, often could provide clues to common medical problems or severe systemic diseases.
This concept remains true for horses and humans today.
Because most horses, however, have darkly pigmented hooves, veterinarians cannot detect the subtle color changes and inclusion bodies that provide human physicians with additional information from nails.
Nonetheless, there are many important pieces of information available to clinicians who look at horses' feet and learn to read the tales of growth, balance, nutrition and the medical history written on the hoof.
Marcella is an equine practitioner in Canton, Ga.