The equine hoof--with its complex arrangement of connective tissues, nerves, cartilage, bone, and blood supply--relies on important nutritional building blocks for strength and integrity.
Photo: Erica Larson, News Editor
The versatile equine athlete depends on strong hooves to be fleet of foot and agile in motion, to negotiate quick turns and abrupt stops, and to absorb impacts sustained by all maneuvers. And the equine hoof--with its complex arrangement of connective tissues, nerves, cartilage, bone, and blood supply--relies on important nutritional building blocks for strength and integrity.
Mary Beth Gordon, PhD, an equine nutritionist at Land O'Lakes Purina Feed, weighed in on factors that influence hoof health: "Genetics is most important, followed by nutrition, then exercise and season. Farriery practices are also significant. Because some horses are genetically endowed with phenomenal hoof strength, even with a less-than-adequate diet their hooves remain strong. However, a severely restricted or poorly balanced diet could adversely affect genetically superior hooves, just as such imbalances negatively impact overall health."
Gordon pointed out that sedentary horses tolerate nutrient deficiencies or imbalances better than active, performance, or breeding animals.
"All horses in all life stages are susceptible to deficiencies and subsequent deleterious effects," said Gordon, noting that early and late life stages are particularly important times to monitor your horse's diet. For example, "The aging digestive system of a senior horse may be less efficient at absorption or production of nutrients in the hindgut, such as B vitamins," she noted. "Supplementation with (this and other) constituents that target the hoof may benefit senior horses."
The Building Blocks
"Protein and energy (including glucose and fatty acids) have important roles in hoof health due to the hooves' structural makeup of protein and keratin (the main fibrous component of hair and hooves)," reported Gordon. "Adequate energy is required by all equine tissues for optimal growth and development; hooves require relatively large amounts of readily available glucose compared to other tissues. Other nutrients such as fatty acids, vitamins, and minerals are also important."
Proteins These are comprised of amino acids linked together; digestion breaks these chemical bonds to release amino acids for absorption and use by all tissues. As sulfur-containing amino acids, methionine and cysteine are important hoof structure building blocks, particularly of keratin and cell envelope proteins that create cornified hoof wall. Katie Young, PhD, also a nutritionist at Land O'Lakes Purina Feed, relayed, "Amino acids play major roles as structural components of proteins and enzymes. As an essential amino acid, methionine isn't synthesized in the body, so must be provided in the diet." Consequently, many hoof supplements are fortified with methionine and other sulfur-containing amino acids to support hoof growth and strength. Nonetheless, high-quality protein sources usually supply sufficient organic sulfur to support hoof health.
Young urged horse owners to provide adequate dietary protein containing all 10 essential amino acids, stressing that adding just a few specific amino acids to a diet might imbalance total amino acids and create other problems.
She suggested, "A better ration design contains high-quality protein sources and essential amino acids balanced to other nutrients in the feed--this meets nutritional needs of not only hooves, but all body tissues and functions."
Vitamins With the exception of A and E, vitamins are produced within the body--the horse synthesizes vitamins D, C, and niacin, while other B vitamins and vitamin K are produced by large intestinal microbial residents. Green forage contains abundant vitamins A, D, E, K, and some B vitamins
Vitamin A is a fat-soluble vitamin that plays an important role in cell differentiation and integrity, and there are reports that its deficiency contributes to coronary band inflammation. Vitamin A deficiency might occur alongside zinc deficiency. (Editor's Note: Read more about vitamin function in horses in The ABCs of Vitamin Nutrition.)
Biotin This is a key component of hoof supplement products--it is a water-soluble B vitamin normally produced in a horse's hindgut and used to form a cementing substance for cell adhesion during hoof wall cornification. "Controlled studies (investigating biotin's effect on growth rate and hoof quality) show contradictory results, yet despite this confusion, many horses receive biotin supplements," said Gordon. "Many owners believe that biotin shortens 'renewal time' of the hoof capsule (how long it takes for the hoof to grow out completely). Studies demonstrated that biotin remedies defects in the structure and horn of the hoof (Kempson, 1987) and in cases of disturbed horn elasticity (Wintzer, 1986)." Reported biotin dosages can be as high as 60 mg/day, but typically they are in the 10-30 mg/day range. It usually takes five to nine months for positive results to manifest in weak, misshapen, crumbling hoof horn, according to researchers.
Gordon noted that no controlled studies establish dietary requirements for biotin above that produced by intestinal synthesis. "While biotin supplementation may help some horses, it is not required by most," she said. "Commercially manufactured feeds containing quality ingredients include naturally occurring biotin."
Biotin also is found naturally in grains, bran, and yeast.
Copper A copper-dependent enzyme, thiol oxidase, is required for building disulfide bonds in keratin. Copper, therefore, affects the strength and rigidity of the outer hoof wall's fully cornified cells and is an important component of antioxidant enzymes that protect cell membranes. "All natural feedstuffs contain copper, but sometimes not in concentrations to meet equine nutritional requirements--especially in hay," reported Young. "Most fortified commercial feeds contain copper that meets equine dietary requirements."
Zinc Young said this mineral is required for "maintenance, repair, and reproduction of epithelial (outer surface tissue) cells, including hoof wall epidermal cells. Zinc is a component of enzymes necessary for synthesis of keratins, keratin-associated proteins, cell envelope proteins, collagen, and lipoproteins, all contributing to hoof strength and function. Zinc also has an antioxidant role." Like copper, zinc is found in all natural feedstuffs, but it might be found in less-than-adequate amounts in hay; it is best supplemented through fortified feeds.
Manganese This mineral is important to chondroitin sulfate synthesis that's integral to joint cartilage maintenance and bone matrix formation; therefore, it contributes to internal foot structures' health. Manganese is also an antioxidant. Forage is a manganese source, along with dietary supplementation when no provided in adequate amounts.
Selenium There have been reports of equine selenium deficiency diseases in 46 states, and they have been correlated with soil selenium content. Young describes selenium's role in hoof health: "Selenium is an essential mineral, a component of an enzyme (glutathione peroxidase) that aids in cell membrane protection." Selenium works in tandem with vitamin E as an antioxidant. Because selenium deficiency leads to impaired immune responses, it is not uncommon for horse owners to feed selenium-fortified supplements. "But," Young noted, "excess supplementation can lead to toxicity with severe symptoms."
Chronic selenium toxicity is evident in horses with noticeable thinning of mane and tail, and these animals eventually develop significant horizontal cracks below the coronary band. If uncorrected, toxicity can cause the hoof's laminar attachments (which connect the coffin bone to the hoof wall) to separate, resulting in painful hoof sloughing that can necessitate euthanasia.
"In areas with high-selenium soils and selenium-accumulator plants, it's best to keep horses off pasture and instead feed hay brought in from other areas and/or offer complete feed with built-in forage," Young advised.
This is an example of why it's always important to consult your veterinarian or a nutritionist familiar with your geographic area when designing your horses' diets.
Calcium This mineral is necessary for cell-to-cell attachment within hoof horn and for metabolism of intercellular lipids. Natural feedstuffs contain calcium, but grains contain higher amounts of phosphorus than calcium--this can inhibit calcium absorption. Young noted that forages with acceptable calcium-to-phosphorus ratios (never less than 1:1) might not sufficiently balance inverted ratios created by feeding unfortified grains.
Essential Fatty Acids
Fats create a necessary barrier to prevent permeability in the hoof--intracellular lipids assist in cell-to-cell adhesion to keep bacteria and fungi from penetrating hoof horn. "Diets containing adequate levels of fat are beneficial to the hoof, but specific fatty acid requirements are not yet defined for horses," said Young.
Laminitis and Nutrition
Nutrition's impact on hoof health is notable when too much energy intake leads to laminitis, particularly in insulin-resistant horses that are at high-risk for developing the debilitating disease.
As an advocate of pasture management strategies to prevent or control obesity-associated and/or insulin-resistant laminitis in horses, Katy Watts remarks, "New findings about cellular structure (histology) of insulin-induced laminitis (-affected hoof wall) encourage us to reevaluate hoof wall rings or ridges and stretched white lines previously considered as caused by 'just a change in diet.' Laminitis related to insulin resistance is different from that seen with grain overload--it has slow, subtle, and cumulative effects."
Owners and veterinarians can help prevent and resolve laminitis by recognizing predisposed horses, identifying signs of the condition early, performing insulin testing, and implementing appropriate nutritional management.
Pasture grass varies in nutritional content and can be another nutritional factor in laminitis development. "A horse on pasture is affected by huge seasonal fluctuations in nonstructural carbohydrate (NSC) content of grass," Watts explained. "When days are sunny and nights are warm, plants have highest NSC levels in late afternoon; lowest levels occur just before dawn. On cloudy days NSC may not increase much at all."
As nighttime temperatures fall, plants stop growing and no longer use up their sugars. Watts continued, "Most cool-season grasses contain three times more NSC when subjected to two weeks of freezing nights."
Watts encouraged owners to pull high-risk horses completely off pasture when nights are near freezing, leaving them off until grass is growing again. Winter rain or melting snow can leach NSC from brown, dead grass. "However," Watts noted, "don't assume dead grass is safe. It's best to sample test for levels of water-soluble carbohydrates (fructan and sugars) and starch."
Watts suggested other strategies to control laminitis risk: "Mow grass before it heads out with seed." Also, "Don't let nutrient levels drop so low that growth slows--such stress increases NSC concentration. Application of fertilizer can double grass production and halve its sugar content; since sunlight makes sugar in plants, thick, taller grass is lower in sugar content than thin, short grass.
"There isn't any 'one size fits all' program for grazing laminitic horses," she said, "because each horse has a different metabolic profile." Exercise amount and intensity play huge roles, as do dietary constituents besides pasture. Watts monitors fat deposits on her horses vigilantly and watches them trot daily: "When the 'neck-ometer' becomes cresty or my normally big-trotting pony starts to shuffle and trip, I restrict pasture completely."
Equine nutritionists advocate adding a concentrated source of all essential nutrients (adequate protein, vitamins, and minerals) to support all body functions. However, consult your veterinarian or nutritionist before making major dietary changes, and be wary of oversupplementation. Horse owners should remember that it will take time following dietary modifications for new, healthy horn to reach the ground surface with appreciable results.
About the Author
Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her recent book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care (available at Shop.TheHorse.com or by calling 800/582-5604). She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.
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