Over Supplementation of Nutrients in the Equine Diet
Excessive supplementation of any nutrient, even if the nutrient is not toxic, requires metabolic and organ functions in order to eliminate the nutrient from the body. This is a waste of valuable resources whether in the form of enzyme activity, energy, or organ usage such as the kidneys.
The risk of over-supplementation increases when adding supplements to a horse’s diet of nutrient-rich forages and fortified feeds. Since most nutrients are correlated with others, too much of one nutrient can create imbalances of other nutrients.
The best known example of a nutrient correlation is the calcium to phosphorus ratio (Ca:P ratio). Calcium and phosphorus are two nutrients that have inverse correlations to each other. The importance of this ratio has been supported by research and from a lesson learned many years ago in equine nutrition.
High Bran Diets
Before the advent of modern grain processing, horses of the grain millers often developed a condition known as “Big Head” or “Miller’s Head”. These horses turned the large stones to grind the whole wheat into flour. The bran, or wheat hulls, was a non-marketable by-product of flour production. The millers found that the horses could derive energy from feeding the otherwise unusable bran to “do work” and maintain weight. Nutrition problems arose from the high phosphorus content of bran. The resulting calcium to phosphorus imbalance created a calcium deficiency, leading to the body removing calcium stores from the bones. The bones of the skull showed the effects of demineralization first. The loss of bone calcium resulted in softening of the joints, termed the “sutures”, where the skull bones joined. The separating skull bones created an enlarged appearance of the head, thus the term “Big Head Disease”.
High bran diets will lead to hoof problems prior to the development of Big Head. The high phosphorus diet interferes with proper formation of the calcium bonds, or “desmosomes”, between the individual cell walls within the hoof tissue. The resulting loss of hoof wall strength creates holes and defects that allow the penetration and proliferation of the bacteria and fungi associated with crumbling hoof horn and White Line Disease.
Just as calcium and phosphorus have a ratio (Ca:P) that they need to fall within, most other nutrients have ideal correlations too. For example the ratios between sulfur, copper and zinc are also important. If too much sulfur is given without a concurrent increase in the correlated nutrients, the excess sulfur can create imbalances and have a detrimental effect on connective tissue and hoof quality.
Dr. Susan Kempson is a noted equine nutrition researcher in the Department of Preclinical Veterinary Sciences, Royal School of Veterinary Studies, at the University of Edinburgh in Scotland. Dr. Kempson has conducted numerous electron microscope studies of the equine hoof wall. Electron microscopes use electrons rather than light to capture images and can magnify up to approximately two million times. The poor hoof condition in Dr. Kempson’s image was caused by over-supplementation of selenium. Dr. Kempson demonstrated with scanning electron microscope photos that a horse that had been supplemented with excessive selenium developed a lack of structure in the hoof horn. Sulfur is required to build the strong cross links necessary for healthy hoof horn, however excess selenium substitutes in place of sulfur creating weak hoof structure. Visible signs include prominent horizontal hoof wall ridges or cracks, a “crusty” coronary band, and hoof wall invasion by bacteria and fungi.
Over-supplementation is a common problem facing horses in the modern world. It is of utmost importance to maintain correct ratios between all nutrients to prevent one nutrient from interfering with the absorption and utilization of another. The more supplements we add to a horse’s diet, the more important it becomes to analyze the diet for proper nutrient correlations. When balancing diets it is just as important to prevent excesses as it is to correct deficiencies.
J. Frank Gravlee, DVM, MS, CNS
Founder of Life Data Labs, Inc.
Developer of Farrier’s Formula®
H. Scott Gravlee, DVM, CNS
Equine Nutrition Consultant