by Dr Derek Cuddeford, Royal (Dick) School of Veterinary Studies, University of Edinburgh
Everyone knows the old saw “No hoof, no horse”. This is rather misleading as the hooves per se are not solely (no pun intended) responsible for problem feet eg., navicular; there are other issues to consider. There are a number of diseases of the feet including corns, laminitis, sand cracks, navicular, abscesses, white line disease and thrush. Of these problems, feeding affects few although management can have a large impact as in the case of thrush. Laminitis and sand cracks are most affected by nutrition and the ability of the hoof horn to “hold” a shoe depends on its structure.
There is a marked difference in weight-bearing between the forelegs and the hind legs because the horse’s weight is unevenly distributed as a result of the protuberance of the head and neck. Thus, the forelegs carry 60% of the horse’s weight so you can imagine the loading of each leg when a 500kg horse jumps a fence; it is 150kg per leg! Think of the size of a hoof belonging to a 500kg horse and compare it with the area covered by your own shoes. For a fairly hefty 80kg adult the loading is only 40kg per foot; roughly 25% of that a horse carries! The concussive forces on a horse’s legs and hooves are enormous.
What constitutes healthy hoof horn? For starters, the water content of the different parts of the foot are key to well being. For example, optimal figures would be 17-24% in the wall, ~33% in the sole and ~50% in the frog. Reduction in the water content of the wall weakens it so stabling horses on sand is probably not advised. However, some recent research throws doubt on this. Feral horses coming from three very different environments, wet and boggy, partially flooded and constantly dry desert had the same degree of hoof wall hydration (29%). Dry or soaked forefeet from Quarter horses showed no differences in terms of hydration! Poor quality softer horn has a higher water content. It has been shown that the water content at the coronary band of ponies was 29% and 27% at the tip of the toe. This was associated with a 30% increase in hoof strength. Thus one can conclude that the tensile properties of hoof wall are profoundly influenced by hydration status.
Hoof growth is affected by a multitude of factors. Protein and amino acids, energy intake, calcium, zinc, vitamin A and biotin largely represent the nutritional factors. But of course, there are many other influences such as environment, hydration, farriery, age, genetics, nature of exercise, work surface and of course breed.
One of the most obvious nutritional influences is that of energy intake. Sub maintenance feeding will result in shortages of nutrients to support hoof growth which will be much slower as a result; hoof strength is unaffected. The classic change in hoof growth is seen when horses are turned out to grass and presented with an excess of feed. At this time hoof growth takes off but of course they receive not just an oversupply of energy but also a bonus supply of nutrients. Growth rates can be 50% more at grass compared to limit-fed animals.
Since hoof horn contains more than 90% protein dietary levels will be important together with constituent amino acids. Some research has demonstrated a linear relationship between cystine content and hoof hardness in normal horn but not in poor horn. Quality horn contained higher levels of a number of amino acids. Supplements for feeding to horses with problem feet often contain methionine, a sulphur-containing amino acid but it is not the silver bullet. It simply acts as a precursor for cysteine which is essential for the formation of good horn. Protein-deficient diets cause splitting and cracking as well as slower growth. Thus it will be apparent from the foregoing that to avoid problem feet one must ensure adequate intakes of both energy and protein. There is no need to worry about individual amino acids provided the diet contains good quality protein such as found in alfalfa.
Some years ago work at Edinburgh Vet School showed that provision of alfalfa to horses with biotin-unresponsive brittle feet caused significant improvements in hoof quality. However, the question remains, was it the additional protein or, the additional calcium? In view of the low cost of calcium it would be negligent to provide diets low in the mineral particularly as it is essential for good bone growth.
Zinc always receives lots of attention but is it worth it? It is of course considered essential for the integrity of the skin, hoof and hair but supplementing already zinc sufficient diets is unlikely to have any beneficial impact. Some German research raised the possibility that there may be individual differences in the ways that horses “handle” zinc. It maybe that there are differences in absorption and utilisation but unfortunately we cannot identify these animals. Many trace elements are sold in a bound organic form or chelate on the basis that there is better absorption etc. Several studies in the USA have failed to show a difference between inorganic and organic sources of trace elements in terms of hoof benefits so do not believe the hype and save yourself some spondulicks… Essentially it is not worth supplementing the diet of the horse that has problem feet with expensive trace elements provided the diet is adequate for all nutrients.
Vitamins play a role in hoof horn quality. A significant role for vitamin A is in the maintenance of the epithelium and thus may have a function in the hoof. It is considered necessary for normal hoof growth but in practice it is highly unlikely that horses will be deficient in A. Horses can store it in the liver and consume bucket loads of the A precursor, β-carotene when grazing green grass. The vitamin that has received much attention is biotin. Studies have shown that this vitamin can increase the growth rate of hooves. Disappointing results have sometimes been obtained when sub-optimal levels of the vitamin have been used. A study in Edinburgh at the Vet School obtained significant improvements in hoof growth as a result of biotin supplementation. However the level used was 0.12mg/kg bodyweight, so for every 100kg, 12mg should be fed and a 450kg horse would require 54mg/day which is way over recommended levels of ~15mg/day. Hoof horn condition improves after biotin supplementation. However, this is not a quick fix and it can take several months to see any real improvements; there is no clear timeline for this effect to become apparent. Thus in reality 15 to 20mg biotin should be fed daily to a 500kg horse for at least one year. This is an expensive undertaking bearing in mind some horses do not respond. A properly balanced diet would meet biotin requirement dispensing with the need for expensive supplements.
In conclusion there are no quick fixes when it comes to hoof care. Listed earlier were a number of factors both nutritional and non-nutritional that affect hoof condition so it is a question of managing these diverse factors to get a good result. Everything must be in synergy. Get the farriery right and the nutrition wrong and both you and the horse have a problem and probably starting a blame game. Causation of problem feet is multifactorial so all affecting factors must be integrated.