In horses, nutrient deficiencies may be primary or secondary. Primary deficiencies result when the diet contains inadequate amounts of one or more nutrients. Starvation can occur when feed resources are scarce, producing a deficiency in calories, protein, and nutrients.
Primary deficiencies in nutrients occur with improperly balanced diets, and secondary deficiencies occur when the diet is nutritionally adequate, but other factors affect nutrient intake or absorption.
© 2008 by Louis New window.
Primary deficiencies in specific nutrients, such as vitamin E, occur with improperly balanced diets. Secondary deficiencies occur when the diet is nutritionally adequate, but some other factor affects nutrient intake or absorption. For example, starvation can occur if a horse is unable to eat due to a mouth injury, even though feed is available.
Secondary deficiencies may be caused by dietary substances or medications that interfere with the absorption of a specific nutrient. Excessive concentrations of dietary zinc inhibit copper absorption and lead to copper deficiency in growing horses despite adequate dietary copper.
From a nutritionist’s perspective, identification of dietary deficiencies requires a diet evaluation. This involves determining the amount and composition of the feeds provided.
Commercial feed laboratories offer affordable and rapid analysis for many important nutrients including protein, calcium, phosphorus and several trace minerals. In contrast, selenium, iodine, and most vitamins require a specialized laboratory.
It is important to remember that most nutritional deficiencies manifest after months to years of dietary inadequacy. Therefore analysis of the current diet may not necessarily reflect a past diet.
Due to variation in nutrient pools within the body and stability of various minerals and vitamins, laboratory submission of whole blood, serum, or liver may be required.
Prior to sample collection, the laboratory should be consulted to confirm the type of sample needed and the optimal conditions for shipping samples to the laboratory.
In the Equine Disease Quarterly, Dr. Carrie Finno indicates that baseline concentrations of circulating vitamin E may indicate the need for supplementation.
However, blood concentrations are not useful in assessing the status of many nutrients. For some, homeostatic mechanisms maintain relatively consistent blood levels, even in the face of significant dietary deficiencies.
For nutrients such as selenium, indicators of functional status may be more useful than serum selenium concentrations alone.
Even for nutrients whose levels fluctuate in the blood with dietary intake, a blood level is only useful if it can be interpreted in relation to horse health.
Laboratories should have established or referenced normal ranges to evaluate blood mineral or vitamin concentrations. Ideally, reference ranges should be developed from normal healthy horses of different physiological states, as age and physiological function (gestating, exercising, growing) affect nutrient needs.
Unfortunately specific reference ranges for blood constituents in equines are very limited. Horses are often described as fragile, but they are also extremely resilient and adaptable.
Horses evolved to deal with times of food abundance as well as food scarcity. Short periods of food scarcity may result in nutritional deficiency; food abundance allows for restoration of body reserves.
Clinical diseases only typically will develop as a result of chronic deficiencies. In addition, overzealous feeding and supplementation can have negative consequences on horse health.
For this reason, dietary changes, even those aimed at correction of nutritional deficiencies, should be made gradually. Perhaps, optimal horse feeding is more like the tortoise and less like the hare.
Press release by Equine Disease Quarterly - Article by Laurie Lawrence, PhD Department of Animal and Food Sciences University of Kentucky