by Dr. Susan A. Kempson
The influence of diet and dietary supplements on the structure and growth of the equine hoof horn has received the most attention to date, although there are still vast areas that are not fully understood. In the study of the effect of nutrition on the structure and growth of the hoof horn, trimmings removed from the foot during routine farrier attention have been used. There is usually a plentiful supply of tissue and its collection is non-invasive and causes no trauma to the animal. Hooves of horses with poor horn have a slow rate of growth, but slivers of horn only 1 mm in thickness can be examined. The hoof samples are processed for both transmission and scanning electron microscopy. Electron microscopy of hoof trimmings has also proved to be a useful diagnostic tool for horses with poor hoof horn growth.
The first report of a dietary supplement helping horses with brittle and friable horn came in 1984 with the work of Comben and others, who illustrated the influence of biotin on the gross appearance of the hoof capsule. These observations were carried out on just three horses and one of these failed to maintain the improvement during the winter. The adult horse is said to have no dietary requirement for biotin (Leighton-Hardman, 1980) unless under stress conditions such as intense work, travelling, being stabled for long periods or being fed low quality diets. This is certainly the case in the author’s experience. Horses which respond to biotin supplementation are those exposed to the stress of top class competition or very young horses in poor bodily condition. Horses which respond to biotin supplementation (approximately five per cent of those with poor quality horn) show large holes in the outermost layer of the wall. The inner layers of the wall were not usually affected. After nine to 12 months of biotin supplementation, the normal tubular structure was restored. Professor Geyer (personal communication) showed that it took 19 months for the structure and mechanical properties of the Lipizzaner horses in Austria to improve significantly. Other factors, such as diet and environment, were not monitored, so it is difficult to know if the biotin alone created the improvement.
It became clear that many horses with brittle, poor quality horn did not respond to dietary supplementation with biotin. Many of these horses did show a dramatic improvement in hoof horn quality when their diets were balanced for calcium. Calcium is known to be essential for the cohesion of cells one to another, particularly in the stratum corneum of keratinised epithelia. The traditional British diet of oats, bran and hay contains low levels of calcium and high levels of phosphorus as phytate. The phytate will block the absorption of calcium in the small intestines and reduce the amount available to the horse.
In the scanning electron micrograph, the structure of the outermost layer of the wall is often normal, but the middle, inner layers of the white line show a loss of normal tubular structure. The individual squames show a loss of normal adhesion to one another. A change of diet to improve the calcium:phosphorus ratio produced a dramatic change in the appearance of the horn within three to four months. Horn tubules interspersed with intertubular horn could be seen. By nine to 12 months, tightly packed squames formed horn tubules and strong intertubular horn.
One of the best ways to improve the calcium:phosphorus levels in the diet is to omit bran completely, reduce the grain component in the diet and replace them with alfalfa. In Great Britain, we can buy chopped alfalfa which can be fed as part of the hard feed ration. Alfalfa is high in protein and calcium and low in phosphorus. A higher percentage of the available calcium is absorbed through the intestines than from Timothy hay (Cuddeford and others, 1990). A further study using a group of riding school horses at the Veterinary Field Station compared the effect of replacing half the hay ration with alfalfa. Apart from hay, the horses were fed oats and horse and pony nuts (a pelleted commercial foodstuff) and had a bran mash on Sundays. None of the horses showed hoof horn defects at the start of the study. The horses were stabled for nine months and worked in the indoor riding school. Every six weeks, the horses were shod and all the hoof clippings were collected, weighed and examined. Over the nine month period, the horses receiving the alfalfa produced 22-25 per cent more horn than the horses on the traditional diet. The structure of the horn from horses receiving the alfalfa showed a slight improvement in quality which was then maintained. In contrast, the control group of horses showed a slow decline in hoof horn structure over the nine months. Two of the control horses started to experience frequent shoe loss and crumbling of the wall. The feet of these two horses improved when they were turned out to grass in the summer.
In the early 1980s, an American veterinary surgeon, Dr. Frank Gravlee, approached the problem of brittle horn in horses from a different angle. He performed extensive blood chemistry analysis on 300 horses and noted the components below average in those horses with poor quality hoof horn. Horses with weak and brittle horn would be low in more than one nutrient, but not all horses were the same. With this information, a dietary supplement called “Farrier’s Formula” was developed to help horses with hoof horn defects. Trials in the United States showed the product was highly effective in restoring horn of good quality and strong functional integrity. A long term trial in Great Britain (Kempson, 1990) showed a progressive improvement in the gross and microscopic structure of the horn. The improvement in the white line could be seen as early as six weeks.Poor quality hoof horn makes the horse very prone to bruising of the foot. This mechanical trauma causes inflammation of the coria and disruption in the process of keratinisation, leading to more poor horn. Supplementation with “Farrier’s Formula” will break the cycle of deterioration and stimulate the growth of good quality horn to protect the underlying tissues.
There is the mistaken belief that if something does you good, a lot will do you much more good. In the case of methionine, which is an essential amino acid, excess is highly toxic. Dietary supplements high in methionine, but not balanced for zinc, copper and iron, will actually cause deficiencies and poor horn. In excess, methionine will block the absorption of zinc, copper and iron. A deficiency of zinc will result in a defect in the horn, known as parakeratosis, or incomplete keratinisation. Supplementation with dietary zinc will reverse the defect.
As information about suitable diets became widespread, horse owners fed a diet well-balanced for calcium and supplemented the diet with “Farrier’s Formula”, but still some individuals failed to show improvement. Careful monitoring of these horses showed some improvement in the organisation of the horn with an improvement in diet. However, all the horses showed infection with either a fungus or bacteria or both. It is thought that these microorganisms are opportunists, as they are found on the surface of normal, good quality horn. They only invade the horn when it has been compromised in some way. Greasy hoof dressings seal in the microorganisms and create an ideal anaerobic environment for their proliferation. The numbers of microorganisms have to be reduced before the dietary effects can be fully realised.
The general advice to horse owners of horses with poor quality horn and to those who wish to preserve their horse’s feet is as follows:
- ensure the diet is well-balanced for calcium. The inclusion of alfalfa and/or sugar beet pulp provides readily available calcium for the horse;
- feed a specifically designed supplement, e.g. “Farrier’s Formula”. Avoid feeding more than one supplement to avoid excess;
- the addition of two to six tablespoons of vegetable oil can be beneficial;
- if the horse is prone to laminitis, avoid feedstuffs high in molasses, maize and peas, the “coarse mixes”;
- avoid hoof dressings, as these can compromise the natural waterproofing mechanisms of the foot;
- make sure the horse has plenty of dry, clean bedding. Deep litter (deep manure!) should be avoided.
Comben, N., Clarice, R. J., and Sutherland, D. J. B. (1984) Veterinary Record 115, 642.
Cuddeford, D., Woodhead, A., and Muirhead, R. (1990) Veterinary Record 126, 145.
Kempson, S. A., (1990) Veterinary Record 127, 494.
Leighton-Hardman, A. C., (1980) Equine Nutrition. London, Pelham Books.
Dr. Susan A. Kempson
Royal School of Veterinary Studies
University of Edinburgh, Scotland