The healthy hoof
The hoof capsule is a masterpiece of biological engineering, which functions to protect the internal structures, absorb concussion, and resist wear from the ground surface. The hoof capsule is a highly specialised structure that is an extension of the outer layers of skin. Experts have tried to come up with a description of the ideal hoof, but studies on Australian wild horses (brumbies) have shown that their hooves adapt to their environment and the total miles they travel between water and grazing areas and a variety of different shapes and lengths appear to be normal.
All the horny parts of the foot have a corresponding sensitive structure from which the hardened outer tissue is produced. These structures are generally called ‘corium’ (e.g. coronary corium, sole corium) and are innervated and vascular (have a blood supply).
Hoof wall horn is produced at the coronary band from tiny projections called papillae, each of which produces a horn tubule. The tubular structure increases the tensile strength of the hoof wall. These tubules are bonded together by intertubular horn, and as they grow down to the ground, they become flatter and hardened by keratinization. The latest thinking is that the lamellae within the hoof also produce both tubular and intertubular horn and the papillae at the coronary band primarily act as a nutrient delivery system to the horn.
It takes between 6 and 12 months for the horn to grow from coronary band to ground, depending on the nutrition of the horse and the health of the foot.
The hoof wall is held onto the pedal bone (the foot bone) by hundreds of interlinking leaves – the sensitive laminae on the pedal bone side and the horny laminae on the hoof wall side. These leaves are called lamellae and allow the hoof wall to grow down away from the pedal bone. The attachment of the lamellae is incredibly strong in a healthy hoof, but they can be comprised by a variety of factors in a case of laminitis.
The sole is produced from solar papillae in the solar corium, the sensitive area just under the sole. The horn is somewhat similar to hoof wall in much of the sole, apart from the more highly keratinized less hard and more rubbery frog. The sole and the frog are meant to bear weight and will stay more healthy if they do.
Inside the hoof capsule lie the internal structures of the foot, including the digital cushion, a large elastic, fatty piece of tissue that helps absorbs concussion and has a protective role, the pedal bone and the lateral cartilages. As the weight is transferred down the horse’s leg to the foot, the digital cushion compresses and the whole hoof expands a little.
Hoof horn composition
The hoof horn consists mostly of a protein substance called keratin. Keratin itself is made up of amino acids (the building blocks of protein), in the form of strong fibres embedded in a matrix, with sulphur cross links holding them together. It takes up and loses moisture and its fibres increase in length with full hydration. The sulphur-containing amino acid cysteine (made in the body from the essential amino acid methionine) makes up about a quarter of the amino acids in keratin. The keratinization (or cornification) process involves a gradual flattening, toughening and death of cells that leads to the final horn. The cornification process gives the horn its strength and elasticity and hoof keratin is one of the toughest biological materials known.
The hoof contains plenty of water – about 25% in the horn, 40% in the sole and 70% in the frog, and also fatty substances (lipids) and inorganic substances including minerals. Essential fatty acids are involved in the gluing together of the horn cells and are involved in creating a barrier to too much moisture. The essential minerals zinc, copper and calcium are also key factors in the keratinization process. Biotin, a B-complex vitamin has a role in the metabolism of keratinizing tissues. Vitamin A is important in all tissue growth and selenium and vitamin E are both important antioxidants, which are important for optimal health of all body tissues.
The problem hoof
Any loss of integrity or proper function of the hoof capsule will affect the health of the whole foot, so maintaining the health of the hoof capsule is wise. The most common problems affecting the hoof capsule are:
- Hoof horn cracks
- Poor quality, dysfunctional hoof horn
- Corns (bruises)
- Seedy toe and white line disease
- Sheared and/or collapsed heels
Factors that contribute to poor hoof horn quality including cracks, crumbling, and thinness include:
- Hoof imbalances and past injury (including coronary band wounds and laminitis)
- Poor environment
- Nutrient deficiency
Genetics play a part in the innate structure and function of the whole body, and it’s clear that the hooves are no exception. Some horses seem to have good feet despite a poor diet and a less than ideal environment, and this is probably due to ‘good genetics’. The same goes for poor hooves, and some horses, no matter the care and attention to all the important factors, will never have excellent hooves.
Imbalances from poor trimming and/or shoeing, too long between trimming or shoeing or lack of care can cause chronic hoof horn problems due to a disruption of the biomechanical function of the hoof capsule and resultant abnormal forces. Most experts agree that nailed-on metal shoes have some unhealthy effects on the hooves, but they do give protection for horses whose owners are unable to keep their horses in such a way to keep them sound without shoes, or who genetically, have poor hooves. It is of utmost importance, however, that if shoes are used, they are applied to only well balanced hooves, are changed before too much horn growth (which cause them to unbalance the hooves) and signs of poor feet including contracted heels, flat soles and atrophied frogs are noticed and dealt with sooner rather than later.
In addition to contributing to poor hoof horn growth and integrity, hoof capsule imbalances will also increase the risk of injury to the ligaments and tendons associated with the limbs.
Laminitis, which may be caused by a variety of factors including diet, drugs, toxicity and concussion, involves destruction of the lamellar bond between the pedal bone and hoof capsule. Future hoof horn production and cornification is affected and it may take many months after a bout, before hoof horn quality improves. During the period when affected hoof horn grows out, there is a higher risk of seedy toe and white line disease and good long term aftercare is important to keep the hooves healthy.
Environmental influences are important, and although horse’s hooves can adapt to a wide variety of conditions, chronic wet and muddy conditions will affect hoof horn detrimentally. Horses who are kept barefoot ideally need to live on a similar surface to that they are ridden on. They need to be consistently kept (and/or) ridden on varied surfaces if expected to cope with varied surfaces when ridden.
In a study in the 1990s, researchers found that horses with poor hoof strength had lower zinc levels in their hoof horn and blood. Those with poor hoof horn quality had horn that contained more water and had lower hardness values. It wasn’t clear whether or not their environmental conditions were different. There was an increase in zinc content of the hoof horn after supplementation. Inadequate intake of the nutrients that are essential for hoof horn production will disrupt the cornification process and weaken the ‘glue’ that holds the horn together, resulting in weak, poor quality hoof horn.
Caring for hooves from the inside
It is clear that certain nutrients are particularly essential for optimum hoof horn function and shortages will affect function detrimentally. Deficiencies of nutrients – especially zinc, calcium, copper and sulphur-containing essential amino acids e.g. methionine can lead to hoof horn problems including interruptions in the cornification process. All horses should be fed a balanced diet; the reason that nutrients found in a balanced diet are called essential is that without adequate amounts, deficiencies and associated health problems will result.
Many horses with hoof problems can have these problems cured by feeding a balanced diet. In fact, the nutrients that are most likely to be short in UK kept horses are those that are key for hoof health, including minerals and good quality protein. Hoof horn consists mostly of protein and shortages in essential amino acids will detrimentally affect the hooves. Calcium, zinc and copper are three essential minerals that are key for healthy skin and hoof horn and interestingly UK forage including grass, hay and haylage are deficient in zinc and copper for horses. The B-complex vitamin biotin has been shown to improve hoof horn growth and quality, including hardness, probably via an effect on the cornification process. At least 20 mg daily is required for an effect, which is much higher than the normal balanced diet level of intake.
Another important dietary factor for optimal hoof health is intake of water soluble carbohydrate (WSC – sugar and fructans) and starch. Excess WSC and starch intake seems to cause suboptimal hoof function, probably via an effect on the integrity and strength of the lamellar bond between the pedal bone and the hoof capsule. There are many theories as to how this occurs, but none are proven. Acute high intake of starch can cause laminitis, a condition where the lamellae fail allowing rotation of the pedal bone. Chronic moderate intake of WSC and/or starch can cause insulin resistance, which seems to increase the risk of laminitis, especially in horses and ponies who are not exercised and those who are overweight.
Overweight horses with high body fat levels are also more at risk of laminitis, thought to be via insulin resistance and/or endocrine effects of fat tissue. Certain individuals seem to be genetically predisposed to laminitis because not all fat horses or those kept on ad lib WSC-rich grass are affected. There is much to learn about laminitis and what the specific triggers are.
Optimal hoof health can be difficult for horses kept outdoors during summer in pasture 24/7 in the UK, due to the high sugar and fructan levels in the pasture grass. Grass will usually have to be restricted with strip grazing, track systems or muzzles to ensure a healthy weight is maintained and the hoof horn and lamellae remain healthy.
Certain drugs and toxins can also interfere with the cornification process, thus affecting hoof horn integrity and function. Keeping a diary of treatments is useful to help understand the effects on the hoof capsule.
The first step for helping the hooves from the inside is to feed a balanced diet. If less than the full recommended amount of vitamin and mineral-fortified compound feed (e.g. nuts or coarse mix) then a multi-vitamin and mineral supplement must be fed daily. Forage-only fed horses and ponies must have a mineral supplement during summer when vitamin intake is adequate from grass, and a multi-vitamin and mineral supplement during winter when preserved forage such as hay or haylage is fed.
Horses or ponies who have severely restricted intake, those fed 10 hour-plus soaked hay or those fed straw for more than half their forage ration need to have extra dietary protein, from either a balancer product or a protein concentrate such as soya bean meal.
A balanced diet means a balanced intake of dietary energy to maintain a healthy weight, and moderate amounts of WSC and starch. Regularly exercised horses can probably cope better with a little excess body fat, and higher WSC and starch intakes due to the positive effects of exercise on insulin levels and body glucose handling.
Once all of the above nutrition factors are taken care of, if the hoof horn is still a problem, a specific hoof supplement can be added to the diet. Such supplements should supply methionine, zinc and biotin, and may also supply calcium, and copper. Research has shown that supraoptimal levels of biotin, much higher than normal requirements, can have beneficial effects on hoof horn quality, hardness and growth.
Caring for hooves from the outside
Environment and exercise seem to have profound effects on horse’s hooves. ‘Outside’ factors believed to be important for healthy hooves include:
- Freedom of movement (plenty of turnout)
- Plenty of exercise (as well as turnout)
- Areas of harder ground e.g. gravel or scalpings in turnout for barefoot horses
- A dry area for the horse to stand on to avoid the hoof being on muddy wet ground all the time
Movement benefits the whole body, and probably helps the hooves by stimulating blood circulation and growth, since hoof horn responds to stimulation by growing. A horse stabled for 23 hours out of 24, exercised lightly in an arena, kept on a less-than-clean bed and fed inadequate minerals cannot be expected to have healthy hooves! Whilst stabling can help give respite from wet and muddy pasture during winter, and can help restrict grass intake during summer, it should be limited as much as possible and other more healthy ways of providing a dry surface and restricting grass should be considered.
In winter, the wet, muddy and often relatively mild weather can be challenging for good hoof health. Stabling, pens or gravel/scalping loafing areas can help to give the hooves a dry surface and respite from the wetness. A high level of moisture in the hoof horn is associated with poor quality horn.
Exercise is so beneficial to the hooves probably because the horse evolved to cover many miles daily and the body and hooves function best in this situation. Exercise also causes a more healthy metabolism and endocrine function, including an increase in insulin sensitivity and more healthy body glucose handling. Exercise also helps the horse to maintain a healthy body weight.
If shoes are used, great care should be taken to maintain hoof capsule health by ensuring sole and frog loading and maintaining good hoof balance.
Products to help keep the hooves clean and free from infection can be helpful, providing the environment is healthy in the first place. Hooves are at particular risk of fungal infections, and anti-fungal products can be useful especially during winter when hooves are often in anaerobic (without air) conditions in the mud.
Thrush is a common bacterial and fungal infection of the frog that, if left untreated, can lead to deep infection and lameness. Affected areas should be cleaned and debrided and treated with appropriate antiseptic products. A clean dry area should be provided, and good foot balance, frog loading, plenty of exercise and a good quality, balanced diet should be ensured.
White line disease and seedy toe both indicate less than optimal hoof capsule health, and like thrush, they should be treated without delay to avoid deeper infection. Affected areas should be debrided and treated with antiseptic products and/or foot soaks. As for thrush, good foot balance, correct loading, plenty of exercise (but relevant to the current health of the hooves), and a good quality balanced diet should be ensured.
Products to help maintain optimal hydration of the hoof can be helpful – sealing in moisture in dry summer weather and sealing out moisture in wet winter weather. These products should always be used on top of all the other factors involved in healthy hooves e.g. exercise, hoof balance, a balanced diet and appropriate environment.
The horse’s hooves are a masterpiece of biological engineering, and when they are healthy they work incredibly well. Keeping hooves healthy involves effort in maintaining good balance with appropriate shoeing and/or trimming, providing an appropriate environment, ensuring a balanced diet and maintaining a healthy bodyweight. Understanding how to care for the horse’s hooves from both the inside via nutrition and the outside via balance, environmental conditions, exercise and external products will ensure their peak health throughout the seasons.