Trainer Magazine

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No foot, no horse

Training (NAT)Web Master
The expression ‘no foot no horse’ is one that has stood the test of time, and discussions about hoof shape, horn quality, and foot conformation continue to dominate in the Thoroughbred racing and breeding industry.  Thoroughbreds in particular have a reputation, perhaps undeserved, for poor foot conformation but can frequently experience problems relating to either hoof horn quality or growth rate during their training careers.  An inability to retain shoes, the appearance of hoof cracks, thin soles, white line disease, and brittle or crumbly feet are all practical issues related to horn quality that trainers may experience in some horses.  While it is easy to perhaps appreciate familial traits in foot conformation and hoof shape, experts also suggest that hoof horn quality is also influenced by genetic factors as well as nutrition, environment, and farriery.  Stable cleanliness is also very important, with studies showing that equine feces have a very detrimental effect on hoof horn integrity, especially where the structure of the horn is not robust.   The focus of this article is the influence of diet on the hoof and how this relates to a typical racing ration.  Hooves contain a large amount of protein, roughly 90% on a dry matter basis, and the most abundant structural protein present is keratin, which contains approximately 18 different amino acids.  These chains of amino acids give keratin its primary structure, and the orientation and interconnection of these chains then gives a specialized secondary structure that relates to location and its function.   The hoof tissues are complex and show a high level of differentiation to deliver functionality. For example, keratin in the hoof capsule is rich in disulphide bonds (double sulphur bonds) that bridge two cysteine amino acids to form cystine to deliver hardness and strength, whereas the keratin found in the frog and white line region have less of these disulphide bonds (S=S) and more sulfhydryl bonds (S=H), affording less strength but more flexibility. Methionine is a dietary essential sulphur containing amino acid, i.e. it cannot be synthesized from other amino acids in the body.  Methionine can be converted to cysteine, which is integral to the form and function of keratin, and is a limiting amino acid in the equine diet, together with lysine and threonine.     There are many factors, many of which are unrelated to diet, that affect the rate of growth of hoof horn.  However, like all other tissues, hoof horn requires a constant source of energy, including a supply of glucose.  It is also important that certain key nutrients are present in sufficient amounts in the diet to support and drive hoof horn growth and to maintain its integrity, which in turn delivers normal functionality.  Studies have shown that it takes about 9-12 months for the hoof wall to grow from the coronary band to the weight-bearing surface and so a great deal of patience is required to see any benefit from changes made to the diet.   Biotin is probably the most well-known micronutrient with respect to hoof quality.  It is a water-soluble B-group vitamin, used by most cells of the body when converted to carboxybiotin, a component of many enzymes.  Biotin is found naturally at a relatively low level in some feed ingredients such as alfalfa, soya, and brewer’s yeast and is also synthesized by many of the resident bacteria found in the horse’s intestinal tract.  It is assumed that this bacterially synthesized biotin is available to the horse, as under normal circumstances no supplemental biotin is required. However, this may change where the hindgut environment is compromised and the microbial population sub-optimal, which may be the case in some horses in training maintained on a high-starch diet with limited forage intake.     Horses with poor hoof horn quality or growth may benefit from additional biotin in the diet.   Biotin has been shown to have a positive effect on the intracellular glue or keratin found as an integral part of hoof horn structure. The normal maintenance requirement for biotin in the diet is about 1-1.5mg per day for an average 1,100-pound horse, but studies have revealed that for an improvement in hoof horn quality or growth, the intake of biotin needs to be significantly higher, with levels of 10-30mg per day being cited as beneficial in scientific studies. Typically, between 2-6mg per roughly 200lb bodyweight of biotin has been supplemented in those scientific trials where a positive effect on hoof has been demonstrated over a prolonged period.     Most racing diets will deliver biotin at a maintenance level and are generally not formulated to deliver the higher amount needed to improve hoof horn quality, although there may be exceptions.  Where a higher intake of biotin is advised, supplementation is usually the route taken.  Remember, however, that 10-30mg of biotin is still a tiny amount and so biotin supplements will always be provided on a carrier to ensure that the quantity fed per day is manageable.  As powdered supplements in feed can be problematic for fussy feeders, it is worth using one that is quite concentrated and so delivers the requisite amount of biotin within a relatively small serving. Excessive intake of biotin is not desirable, although, as it is a water-soluble vitamin, any excess will be lost in the urine.   There are many cases where biotin supplementation seems to have no beneficial effect, even when fed over a prolonged period.  This is because where hoof quality or structure is poor, there can be more than one type of defect responsible in the hoof horn.  Dr. Sue Kempson, a noted equine nutrition researcher, showed in the 1980s that it was defects to the outermost layers of hoof horn structure that were most often resolved with biotin supplementation.  In contrast, where there is defective horn on the innermost part of the hoof capsule -- which accounted for 94% of her cases -- biotin was ineffective on its own in resolving the issue.  However, sufficient biotin in the diet in combination with adequate calcium and quality protein to supply important amino acids was more successful in improving this type of defect, according to Kempson’s research.   Much research has also been carried out on the role of calcium in hoof horn structure and growth.  Calcium is needed to activate an epidermal enzyme, or transglutaminase, which is present and active in the cross-linking of keratin fibers and so it is important for cell-to-cell attachment.  Calcium also plays a role in depositing the intracellular lipids in the horn structure, which influences moisture balance in the hoof and the ability to repel bacteria from the environment.  Inadequate calcium in the diet is often characterized by crumbling hoof horn, especially around the nail holes and heels.  Dr. Derek Cuddeford, formerly of the Royal (Dick) School of Veterinary Studies, published work supporting the use of alfalfa or lucerne to improve hoof quality and growth by providing a bioavailable source of calcium, as well as an increased intake of digestible protein, delivering an important source of amino acids.   Zinc is an important trace mineral with respect to hoof structure and it is needed for the optimum activity of near to 200 enzymes in the body, including those involved in keratin formation.  Supplemental zinc has been shown to improve hoof horn quality, but this will only be the case when zinc intake was previously marginal or low.  In cattle, research has suggested that organic or chelated zinc, where the zinc is attached to an amino acid or small protein fragment, is more efficient in this respect, although this has not been studied in horses. It is believed that zinc is particularly important for adherence of the horn cells together with a sort of intracellular glue. A significant effect of zinc supplementation on the growth rate of hair, another keratin-rich structure, has been reported previously in ponies.  In Photo 1, the higher growth rate of mane hair during periods of zinc supplementation in grazed ponies is visually significant when compared with the non-supplemented periods. Copper is also an important cofactor, as it is responsible for activating an enzyme called thiol-oxidase that is involved in the formation of the disulphide bridges in keratin.  Vitamin A is a fat-soluble vitamin that is also needed for the development of horn epithelial tissue, although an excessive intake has a detrimental effect on horn structure.   While selenium is an important trace element needed in sufficient amounts in the diet, an excess of selenium can have a severe effect on hoof horn structure, as selenium has a relatively narrow margin of safety.  Excess selenium in the diet prevents the disulphide bridges being formed correctly with selenium (Se) replacing sulphur (S), making the structures inherently weaker.   The requirement for selenium for a typical 500kg horse is in the range of 1-3mg per day, but there is some controversy as to where the safety margin lies with particular respect to hoof horn structure. The scientific literature suggests that 10mg per day is the upper safe limit for selenium in the diet, while more conservative estimates suggest that this may be nearer to 5mg per day.  Kempson suggests that horses with persistent thrush that do not respond to conventional treatment may be exposed to an excess of dietary selenium. The most severe cases of selenium toxicity can result in the hooves sloughing off like slippers. Selenium intake should certainly be investigated, especially as it is common practice in racing to use multiple supplements, many of which may contain selenium. Most people are aware of the link between excessive or inappropriate nonstructural carbohydrate intake and laminitis.  Non-structural carbohydrates, or NSC, consist of starches and sugars as well as fructans, which are the storage polysaccharide of many grasses.  Starches and sugars would predominantly be digested in the small intestine, while fructans are usually fermented in the hindgut.  When a large amount of NSC reaches the hindgut complex, it is readily and rapidly fermented, leading to significant change in the resident microbial population with associated shifts in pH and mucosal cell permeability. Laminitis can then arise, although the exact mechanism for this remains unclear.  However, the clinical signs of laminitis are unlikely to be a ‘cliff edge’ scenario and there may be deleterious effects on hoof stability long before a laminitis attack is suspected.  Vets at Rood & Riddle in Lexington, Kentucky, suggest that low-grade chronic laminitis is very common in Thoroughbred horses, and that these are the horses that will go unnoticed until further complications arise such as lameness. They also suggest that abnormal hoof growth is a common finding in these cases, with evidence of more heel growth compared to the toe, with a dished dorsal hoof wall and toe cracks. The racing diet may add to the risk of laminitis in some cases, where a very high-starch ration is fed, often exacerbated by large meals which allow an unregulated dumping of NSC into the hindgut leading potentially to chronic hindgut acidosis.  This may also impact the biotin status of these animals, as the numbers of biotin-producing microflora are reduced in the resident population. The rations of most horses in training should provide plenty of protein and so should easily fulfill the requirements for methionine and other important amino acids.  Racing diets are also generally well-fortified with the key micronutrients including calcium, zinc, copper, and vitamin A needed for good hoof quality.  The intake of calcium is usually far in excess of requirements, although the Ca/P ratio can sometimes be a little low, if for example diets are top-dressed with significant quantities of oats.  Maintaining the level of calcium relative to phosphorus is also important, as this may impact hoof horn quality.   The level of biotin is most likely to be present at a standard maintenance dose in most racing rations and so this is the nutrient that is more likely to require supplementation. However, we should always remember that a holistic approach to hoof quality is required with all aspects of management, feeding, environment, and farriery being considered and improved where necessary.     Dr. Catherine Dunnett BSc, PhD, R.Nutr Independent Equine Nutrition  

The expression ‘no foot no horse’ is one that has stood the test of time, and discussions about hoof shape, horn quality, and foot conformation continue to dominate in the Thoroughbred racing and breeding industry.  

Thoroughbreds in particular have a reputation, perhaps undeserved, for poor foot conformation but can frequently experience problems relating to either hoof horn quality or growth rate during their training careers.  An inability to retain shoes, the appearance of hoof cracks, thin soles, white line disease, and brittle or crumbly feet are all practical issues related to horn quality that trainers may experience in some horses.  

While it is easy to perhaps appreciate familial traits in foot conformation and hoof shape, experts also suggest that hoof horn quality is also influenced by genetic factors as well as nutrition, environment, and farriery.  Stable cleanliness is also very important, with studies showing that equine feces have a very detrimental effect on hoof horn integrity, especially where the structure of the horn is not robust.

The focus of this article is the influence of diet on the hoof and how this relates to a typical racing ration.  Hooves contain a large amount of protein, roughly 90% on a dry matter basis, and the most abundant structural protein present is keratin, which contains approximately 18 different amino acids.  These chains of amino acids give keratin its primary structure, and the orientation and interconnection of these chains then gives a specialized secondary structure that relates to location and its function.   

The hoof tissues are complex and show a high level of differentiation to deliver functionality. For example, keratin in the hoof capsule is rich in disulphide bonds (double sulphur bonds) that bridge two cysteine amino acids to form cystine to deliver hardness and strength, whereas the keratin found in the frog and white line region have less of these disulphide bonds (S=S) and more sulfhydryl bonds (S=H), affording less strength but more flexibility.

Methionine is a dietary essential sulphur containing amino acid, i.e. it cannot be synthesized from other amino acids in the body. Methionine can be converted to cysteine, which is integral to the form and function of keratin, and is a limiting amino acid in the equine diet, together with lysine and threonine.