Common factors influencing the quality of the hoof are genetics, environment, farriery and nutrition. The horse’s hoof is made up of or affected by all components of the equine diet, including protein, fat, carbohydrates, vitamins and minerals. Since there is no one nutritional panacea for hoof health, balancing these components (based on the horse’s age and lifestyle) is important for the overall health of the horse and its hooves.
It is also important to review the research that has been conducted on how different nutrients may affect the growth of the hoof. And, to understand how nutrition can help or hinder the hoof, it is essential to understand how the horse digests and absorbs different components of its diet.
The horse has evolved as a continuous grazing, non-ruminant herbivore, although it has a significant capacity for digesting cereal grains. Its digestive track is well adapted to small, high-fiber meals due to the continuous microbial fermentation that occurs in the cecum and colon. The fact that man has domesticated the horse and increased its energy demands has brought about the need to supplement their diet with higher-energy, well-balanced concentrates.
The digestive tract of the horse can be broken down into two systems. The first system, including the stomach and small intestine, is very similar to that of man and dog. The second, the hindgut of the horse, has many similarities to the foregut of the cow.
The stomach of the horse has two functionally different sections. The non-glandular squamous mucosa and the glandular region. The non-glandular region has a population of lactobacteria, which have a small capacity to hydrolyze starchs to lactic acid. Once the ingesta reach the glandular region, the microbial action is halted due to the presence of stomach acid. This gastric acid mixes with the ingested feed and aids in digestion. Food remains in the stomach for approximately 20 minutes. This region of the digestive tract has received much attention recently due to a large number of performance horses that have been found to have gastric ulcers. It is thought that those horses who are allowed to eat multiple small meals a day and keep something in their stomach to neutralize the acid will have fewer gastric ulcers. There is increasing evidence that intensely exercising horses are subject to gastric compression, which may push acid into the squamous region of the stomach. This may be another reason why performance horses develop gastric ulcers in this region (Merritt AJVR 2002).
The small intestine is the site of enzymatic digestion. Since the horse has no gall bladder these enzymes are continuously released from the pancreas. Proteolytic enzymes break down protein into amino acids. Protein is used for muscle tissue growth and regrowth and is not considered to contribute to the excitability of horses. Starch is broken down by the amylolytic enzymes, is absorbed as simple sugars (blood sugar), and stored predominantly as glycogen. Starch can be supplied from oats, barley and corn. Overloads of these grains can lead to laminitis. Glycogen is the primary energy source for short duration, high-intensity anaerobic exercise.
The efficiency of starch digestion is extremely important in the horse. If the small intestine is overloaded with starch from a large concentrate meal, then that starch passes though to the hindgut where it is hydrolyzed by bacteria and results in lactic acid being produced in the cecum. This change in pH can be very detrimental to the horse. It has been suggested that no more than 2g of starch/Kg of body weight be fed to a horse in one meal. Corn has approximately 70% starch and complete feeds (those with the forage portion built in) have about 20% starch (NSC).
Even though the adult horse did not evolve consuming diets with higher levels of fat, it does have a great capacity for fat digestion and absorption once the system has adapted to it. (It must be kept in mind that mare’s milk is 15% fat on a dry matter basis.)
Fats are broken down by lipolytic enzymes and absorbed into the lymphatic system or some are absorbed directly into the blood. Fat is then stored as body fat. The dietary fat-soluble vitamins A, D, E and K are also absorbed in the small intestine in association with dietary fat.
Digestion and absorption in the cecum and colon is dependent upon microbial fermentation. Dietary fiber undergoes fermentation in the large intestine and results mainly in the production of volatile fatty acids (VFAs). The majority of these VFAs are absorbed and converted to glucose or fatty acids, and stored as body fat or glycogen. Propionates being the only VFA that can go through gluconeogenesis and ultimately become glycogen. This pathway is not as efficient in energy production as starch digestion in the small intestine. However, fiber is a significant source of energy for the horse and should not be thought of only as bulk for a healthy intestinal environment.
Protein not digested in the small intestine will enter the hindgut where it is predominantly utilized by the bacteria to perpetuate bacterial synthesis. Very little is utilized by the horse. This is important for foals, broodmares and performance horses because they require high-quality protein in their diet and will need to be fed a ration formulated with a specific amino acid profile.
Starch that enters the hindgut is hydrolyzed by lactobacilli and lactic acid is produced. This acid environment can decrease the fiber digesting capacity of the hindgut and possibly predispose the horse to impaction colic. If the pH drops enough it can also set the horse up for laminitis.
The other important nutritional event that occurs in the hindgut is the synthesis of the water-soluble B-complex vitamins (including biotin) by the resident microflora. The body tissues produce Vitamin C. High starch diets can result in impaired fermentation and therefore be detrimental to B-complex vitamin production. Water-soluble vitamins are not stored in the body of the horse. This requires a constant source of vitamin production in the hindgut. This is significant because some horses may require supplementation if hindgut function is suboptimal. B-complex vitamins are thought to affect appetite and therefore horses with impaired hindgut function may have poor appetite and need B-complex supplementation.
Now with a basic understanding of the digestive functions of the horse, we will review the key elements of equine nutrition that are critical to the development of the hoof.
Horses require four basic nutrients in balanced amounts: protein, vitamins, minerals and energy. Excesses or deficiencies of these four basic nutrients can affect absorption and utilization of others.
The element that can change most dramatically is energy. The daily calorie requirement for horses ranges from 16,000 cal/day for maintenance to more than 30,000cal/day for lactating broodmares and some performance horses. The life stage or workload will determine the amount of dietary calories required.
The type of exercise the horse is performing will determine what the horse utilizes as energy. In horses, aerobic exercise performed for a long duration at low intensity typically results in a heart rate of less than 150 beats per minute (BPM). Anaerobic exercise performed for a short duration at high intensity results in a heart rate of greater than 150 BPM.
Horses also have three fuel tanks from which to draw energy: fat, glycogen and protein. Horses can fill those fuel tanks from four sources: soluble carbohydrates (starch), insoluble carbohydrates (fiber), fat (vegetable oil) and protein (amino acids).
Starch is the main source of energy for anaerobic metabolism. Absorption of starch results in elevated blood glucose and is sometimes associated with a “hot” or “high horse.”
Fermentation of fiber (insoluble carbohydrates) in the hindgut results in VFA production. A diet of fiber alone cannot support maximal workloads, especially anaerobic work. The horse cannot fill the glycogen fuel tank from hay alone. A horse performing intense exercise may need a hay-to-grain ratio of 40:60 percent to meet its energy demands. Horses should always be fed at least one percent of their body weight in roughage to maintain proper gut function.
The maturity of hay greatly affects the digestibility. Leaving grass growing even an extra 20 days will decrease the digestibility significantly. Also, if the hay is cut very early, the fiber content can be very low and can cause problems for the horse’s digestive tract. The vitamin content of hay will also decrease with storage time.
Fat is a very energy dense source of calories. It is added to the ration of the horse in order to meet high-energy demands without running into starch overloading. Vegetable oils are very palatability and also improve the hair coat. Fat is the primary source of energy for aerobic metabolism.
Protein is a metabolically expensive source of energy. Horses require certain amounts of protein for different stages of life not certain percentages. Adult performance horses require 40g protein/Mcal of energy. Growing horses require 50g protein/Mcal. Most straight grains will be deficient in specific amino acids like lysine. Lysine is necessary for proper growth in foals so it should be added to balance a feed. Protein requirements increase with exercise but the protein-to-calorie ratio does not. Protein is used to repair and build muscle.
Specific Nutrients Affecting The Hoof
There are several nutrients that can influence hoof growth and quality. There is very little evidence to suggest that the addition of extra nutrients to an already balanced diet will promote hoof growth in the normal horse.
Energy has been shown to affect the growth of the hoof in growing animals (Butler & Hintz 1977). The energy intake was restricted in one group of growing horses while the other group was fed ad libitum. A reduced rate of hoof growth was seen in the energy-restricted group. It is possible that anything that restricts body weight gain will also restrict growth rate of the hoof.
The hoof is predominantly keratin, which is an insoluble protein. Protein deficiency can have the same effect as energy deficiency. The hoof growth of weanlings fed 10% protein was only two thirds that of weanlings fed 14.5% protein. Investigators have failed to show an effect of specific amino acid supplementation on the growth of hooves. Although, if a horse is fed a diet deficient of a specific amino acid and balancing that diet promotes weight gain, then it may also promote hoof growth (Hintz, Current Therapy, 1983).
The amino acid concentration has been shown to be different within the horn of good quality hooves as compared to that of poor quality hooves (Coenen 1997). The essential amino acid methionine is thought to cause depletion of iron, copper and zinc if fed in excess. This can lead to incomplete keratinization and is thought to be associated with crumbling horn and white line disease (Kempson).
Fats are needed by the hoof to create a permeability barrier. Intercellular lipids are essential for creating the permeability barrier in the horn, which also assists in cell-to-cell adhesion (Kempsen and Campbell 1997). Permeability barriers help prevent bacteria and fungi from penetrating the horn. Diets containing adequate levels of fat can therefore be beneficial to the hoof.
A proper balance of minerals is also important in hoof growth and quality. Selenium is important as an antioxidant in the protection of cellular membranes. It is also important in many enzyme systems. Excess selenium in the diet can lead to substitution of sulfur in the keratin fibers with selenium, resulting in little to no structural integrity (Kempson 1998).
Many supplements as well as commercially manufactured diets contain added selenium. There is the possibility of selenium toxicity from over-supplementation. Selenium accumulating plants (e.g. Astralagus spp) in selenium-rich soils can be toxic if consumed by horses. Selenium toxicity can occur when the level in the diet reaches 2mg/kg (NRC 1980). Chronic selenium toxicity can result in hair loss, coronitis and bleeding of the coronary band as well as sloughing of the hoof and even laminitis. A shortage of selenium intake is not associated with the development of hoof problems (Coenen 1997).
Zinc has been shown to be important in the normal keratinization hoof; therefore, inadequate levels can lead to compromised hoof health and quality. Horses with insufficient hoof horn strength had less zinc in the hoof horn and plasma than did horses with no hoof horn damage (Coenen 1997). Zinc deficiency has been associated with reduced growth rate and parakaratosis in growing foals (Harrington et al., 1973).
Calcium and phosphorus and their ratio to each other are related to normal hoof development. Calcium is needed for cell-to-cell attachment in the hoof horn. Calcium is also important in the metabolism of the intercellular lipids. Excess phosphorus can block the absorption of calcium from the small intestine. This can result in a calcium deficiency and a disease called Bran Disease. Bran Disease causes weak and abnormal bones. Calcium deficiency can affect cell-to-cell attachment and metabolism of intercellular lipids. Commercially manufactured feeds are balanced so that when fed with good quality hay the proper Ca:P ratio will be achieved.
There has been a plethora of investigations into the effect of biotin on the growth rate and quality of hooves. Biotin is a water-soluble vitamin that is normally produced in the hindgut of the horse. Controlled studies have had varying results on whether or not biotin supplementation has an effect on the growth of hoof horn. Reilly (1998), Bains (1995) and Buffa, et al., found that biotin supplementation increased hoof growth. Geyer and Schulze (1994) and Josseck, et al., (1995) found no difference in growths rates and Dittrich, et al., (1994) showed a decrease in hoof growth during biotin supplementation.
Despite this confusion many horses are supplemented with biotin in hopes of improving their hoof growth or quality. It is generally accepted that biotin improves the quality of hooves and many do believe that it will shorten the “renewal time” of the hoof capsule.
Dosages for biotin range from 7.5 mg/day to 60 mg/day for a mature horse. The amount of time required for supplementation in order to see results in the hoof also varies from five to nine months. Biotin deficiency has not been reported to cause a problem with hoof development. No controlled studies have been published to establishing a dietary requirement above that which is produced by intestinal synthesis (NRC 1989). While biotin supplementation may help some horses, it is not required by most of the population. Commercially manufactured feeds utilizing quality ingredients will contain naturally occurring biotin. Some feeds formulated for senior horses that may have impaired hindgut function will have added biotin.
Vitamin A is a fat-soluble vitamin that plays an important role in cell differentiation and integrity. Inadequate levels may result in hoof dryness.
To determine if your horse has a good balance of protein, vitamins, minerals, energy and nutrients, a body condition scoring system can be applied.
Body Condition Scoring System
A good method to determine whether or not you are meeting your horse’s energy demands is by using a body condition scoring system. This system ranks horses from 1-9 based on the amount of stored body fat and skeletal muscling. A score of “1” is an emaciated horse. A score of “9” is an obese horse. A score of “5” is considered ideal for an athlete.
Horses that are not working or reproducing may get all the energy they need from good quality hay or pasture to maintain a body condition score of 5-7. However they will not get their mineral needs met from this alone; therefore, they will need a mineral supplement. A trace mineralized salt block is 98% salt and will not meet the mineral requirements. A horse on pasture alone will require a real mineral supplement in block or loose form. A plain salt block should be available at all times also.
When trying to balance a horse’s diet, it must be kept in mind that straight grains alone are going to be deficient in several nutrients. Oats, for example, are a good source of fiber but are variable in protein and inadequate in trace minerals and vitamins. And, feeding horses by volume instead of by weight is a common mistake. A coffee can of oats, corn and a commercially pelleted feed will all weigh different amounts.
In summary, the balance of protein, vitamins, minerals and energy is more important than supplementation of just one of them. The requirements of the basic nutrients will vary between the life stage and or workload of the horse. The horse should be fed good quality roughage at a rate of no less than one percent of its body weight along with a balanced concentrate. These should be fed at a rate to keep the horse at a body condition score of 5-7. If this is done, then you will consistently meet the nutritional needs of the horse while providing for healthy hooves.
Contributed By: Scott King, D.V.M. courtesy of Purina Mills, LLC. (AAEP)