VITAMIN AND MINERAL SUPPLEMENTS FOR HORSES
Vitamins and minerals are often added to a grain mix to ensure it is balanced and meets a horse’s minimal nutritional requirements. A vitamin and mineral premix should be specific for the classification of horse. It is usually added to the grain mix and bound either with molasses in a textured feed or pelleted. The key to using vitamin and mineral supplements is to incorporate them to balance the diet and to avoid over-supplementation.
If you are using a grain mix that already includes vitamins and minerals specifically for your horse’s age, workload, and production status, then you shouldn’t need to top-dress with additional vitamins and minerals. Not only is this an expensive practice, but you are disrupting the diet’s carefully formulated nutrient calculations. Overfeeding vitamin and mineral supplements may create an imbalance in the amount of vitamins and minerals in your horse’s diet. Typically, a horse that is receiving commercially-prepared concentrates (grain mixes) along with good quality forage will receive sufficient vitamins and minerals if the owner follows feeding instructions and feeds the horse according to its age, weight, activity level, and reproduction status.
Evaluating Vitamin and Mineral Status
A horse’s overall health, appearance and performance output can all be used to determine their vitamin and mineral status. However, all of these characteristics can be influenced by many other factors including disease, parasite load, training and overall nutrition.
The first step to determine if a horse is receiving an adequate supply of vitamins and minerals is to evaluate the horse’s overall diet. An equine nutritionist can evaluate the horse’s daily feeding program and, based on science based calculations, determine if the horse is being fed a balanced diet. For the most accurate feed evaluation, the forage (hay or pasture) should be analyzed at a laboratory for a nutrient profile. If grain is being fed, the grain-mix formula needs to be available. The daily amounts of both the forage and grain consumed will need to be measured to determine the horse’s daily nutrient intake. Beyond ration evaluation, blood and hair analysis have been used to estimate nutrient status in the horse.
Some nutrients can be analyzed through blood work. Depending on the nutrient, a veterinarian may need a whole blood, plasma or serum sample for laboratory work. The blood sample needs to be handled with care so that hemolysis doesn’t occur.
In some respects, the blood status of a single nutrient at a single point of time may not give a good picture of the availability of the nutrient to the horse. Deficiency or toxicity symptoms in the animal must also be included in determining if a horse has a nutrient deficiency or toxicity. Some nutrients do not have well- defined blood parameters for equines.
Nutrient-specific enzyme activity can also be measured to try to determine if a specific nutrient is present. For example, glutathione peroxidase has been measured to determine the status of selenium in a horse.
Hair analysis is not a reliable means of assessing the nutritional status of a horse. Hair analysis results can vary based on the color of the hair, time of year, sex, breed, age of horse, and sample site as well as environmental contaminates that the hair has been exposed to prior to testing. While hair analysis may be useful in determining a horse’s exposure to toxic elements, it is not recommended for determining the status of vitamins and minerals in the horse. Diets should not be balanced on information obtained from hair analysis. Nutritional supplements that are recommended based on hair analysis should be viewed with extreme caution.
Figure 1. Hair analysis results can vary based on the horse's coat color and the results should not be used to balance a horse's diet.
Selenium and Vitamin E
The trace mineral selenium and vitamin E are two nutrients that have received a lot of attention by both horseman and equine researchers alike. Both are required by the horse for optimal athletic and reproductive performance. There is an interrelationship between selenium and vitamin E. Both play a role in metabolism as well as being anti-oxidants. In some cases, one can substitute for the other such that a deficiency is delayed. There are some deficiency symptoms that respond only to the supplementation of either selenium or vitamin E.
Selenium (Se) is a trace mineral, an essential nutrient that is an anti-oxidant. It protects the body from oxidative stress. It can, however, be an environmental toxicant. The recommended daily intake of selenium is 1 mg/day. Most commercial grains have .3 - .4 mg/kg of selenium.
Selenium levels vary in the soil based on geographic location. For example, Michigan soil and soil in other states shown darkened on the map below are low in selenium. If your pasture looks great, don't be fooled. Plants do not need selenium and may look great without enough selenium; but if there is not enough selenium in the soil, a horse will not get a sufficient amount from forage or grain grown in that location. Even if the soil in your area is not selenium-deficient, the feed you purchase may have been grown in other states and may not have sufficient levels of selenium. On the other hand, feed grown in other soils may have extremely high levels of selenium, which may cause toxicity problems.
Figure 2. Soil selenium levels in the United States
A selenium deficiency may cause white muscle disease, muscular dystrophy, tying up, reproductive problems, and impaired immunity. On the other hand, chronic (long-term) selenium toxicity (also known as "alkali disease") can cause partial or total hair loss (alopecia) in the mane or tail, erosion of the long bones, and cracking and sloughing hooves. In acute (sudden) toxicity, also known as "blind staggers," the horse may go into severe distress or sudden death may occur. The danger of selenium toxicity was dramatically brought to the horse community’s attention in this year’s Florida polo pony tragedy.
If you have reason to be concerned about a selenium deficiency, a mineral block with selenium may be given to ensure that a horse is getting the recommended intake. Most commercial grains formulated for equine have added selenium at the upper recommended level so that if you feed the recommended amount of grain for your horse’s weight, your horse will receive adequate selenium. However, selenium is toxic in amounts over the recommended daily intake, so make sure you know how much your horse is really getting and how much it really needs before supplementing.
Vitamin E is a fat-soluble vitamin stored throughout all body tissues and in the liver. Since there are different forms of vitamin E, you may also hear vitamin E referred to as tocopherol or tocotrienol, which are both naturally occurring compounds. Tocopherol, especially alpha-tocopherol, has the most nutritional value. The main function of vitamin E is as an anti-oxidant; it works with the micromineral selenium in cell metabolism.
Fresh forage is the best source of vitamin E. Hay cut at an early stage is higher in vitamin E than mature hay; however, vitamin E content rapidly leaches out of stored hay in a few months. Vitamin E concentrations in grain (20 – 30 IU/kg DM) are considerably lower than fresh forage (30 – 100 IU/kg DM). Most commercial horse feeds have vitamin E included in their formulation to allow for the variables in a horse’s diet. RRR-α-tocopheryl acetate, a natural source of supplemental vitamin E, is more available than its synthetic counterpart all-rac-α-tocopheryl acetate.
Vitamin E deficiencies are usually associated with the consumption of poor-quality hay and low concentrations of circulating levels of alpha-tocopherol in the body. Vitamin E may play a role in two neurological disorders, equine degenerative myeloencephalopathy (EDM) and equine motor neuron disease (EMND). Case studies about EDM on large horse farms indicate a genetic component to the disease, predisposing the horses to developing a Vitamin E deficiency. On the other hand, EMND may be directly caused by a vitamin E deficiency in the diet.
While selenium deficiencies in pregnant mares can result in foals with white muscle disease, supplementation of both selenium and vitamin E is used to treat both the mare and foal. Vitamin E supplementation has been beneficial in cases of myositis (tying up), in horses who exercise heavily, leading to increased oxidative stress, and in fat-supplemented diets. Although an excess of vitamin E seems to be less toxic than excesses of other vitamins, it’s wise to stay within the recommended limits until more research is done on the benefits of vitamin E supplementation, unless you are working with your veterinarian on a specific health problem.
Feeding Vitamin and Mineral Supplements
Vitamin and mineral supplements can be used to help balance a horse’s diet, help repair poor quality hooves, and replenish electrolytes lost in sweat due to exercise or a hot and humid climate.
If your horse is primarily receiving its nutrition from hay, then you should consider a supplement that balances for the vitamins and minerals that may not be present or may have leached out of the hay. Vitamins begin to leach out of hay as soon as it is harvested. Vitamins are very sensitive to light and temperature and will begin to degrade over time. The longer the hay has been stored the lower the vitamin content will be. In fact, many nutritionists don’t consider the vitamins present in hay when balancing a ration because of the variability and potential loss over time.
Many new supplements are formulated to make up for inadequate amounts of vitamins and minerals that may occur in an all-forage diet. These supplements may be geared towards balancing a specific type of forage (grass, legume, or mix); some are directed towards different classifications of horses. You should know your horse’s approximate weight and feed these supplements as directed.
Hoof quality (or integrity) also has a link to nutrition. Poor hoof quality beyond poor hoof care can be an indication of poor protein, vitamin, or mineral status. Poor hoof quality is noted by thin, weak hoof walls, or slow hoof growth.
The water soluble vitamin biotin is important in the metabolism of carbohydrates, fats, and proteins. Biotin concentrations are high in alfalfa; intermediate in oats, barley and soybean; and low in corn. Biotin is also synthesized by microbes. There are no deficiency or toxicity symptoms of biotin, and there is no established dietary requirement for biotin in a horse’s diet. Several studies in horses with poor hoof quality (Comben et al., 1984; Kempson, 1987; Josseck et al., 1995; Zenker et al., 1995), however, have demonstrated improvement in horses that were supplemented with biotin at rates ranging from 10 mg – 30 mg/daily over a long period of time (6 – 38 months). It should be noted that a balanced feed ration with quality protein is also important for good hoof integrity.
Good quality, well-trimmed hoof.
This neglected hoof has chips and an improper angle.
Free Choice Salt
Outside of clean water, adequate pasture and/or hay, and the amount of concentrate required for your horse’s level of activity or growth, the best recommended supplement is free-choice salt. Salt is a commonly added ingredient of formulated grain mixes; however, because horses will more or less self-regulate their salt intake, and needs may increase with sweating, it is a good idea to provide horses with easy access to salt blocks.
Salt can be purchased in several forms: small blocks (two pounds); 50-pound blocks, and loose. Some studies have shown increased consumption of salt and minerals from the loose form in contrast to the blocks; however, blocks are usually easier to feed outdoors. Some owners prefer to offer free-choice salt and minerals only in a pasture or paddock. A stalled horse may consume salt out of boredom, leading to an increased water consumption and subsequent increased urine excretion.
Many owners prefer to purchase trace-mineral salt. Trace minerals are those required in very small amounts by the animal in contrast to macrominerals which are required in larger amounts. Trace mineral salt is primarily salt (98% sodium chloride) with a small fraction of trace minerals--zinc, manganese, iron, copper, cobalt and iodine.
While all horses can benefit from a salt supplement, it is vital to provide salt or trace mineral salt free-choice to horses that live in hot and humid climates and/or are worked hard. In their sweat, horses will lose electrolytes; they must be replaced by eating additional dietary salt. Horses performing hard work such as endurance competitions may benefit from additional electrolyte supplements. For more information, please see Dr. Hal Schott’s article on "Do Electrolytes Really Help During Endurance Exercise?"
Over-supplementing vitamins and minerals is costly, and in some cases can be toxic to a horse. The best practice is to provide a well-balanced diet that includes the recommended amounts of the various vitamins and minerals for your horse’s age and performance requirements. Consult with your veterinarian or equine nutritionist before supplementing a horse. Some vitamin and mineral supplements can be counterproductive to certain health problems.
References and Additional Resources
Comben, N., R.J. Clark, and D.J.B. Sutherland. 1984. Clinical observations on the response of equine hoof defects to dietary supplementation with biotin. Vet. Rec. 115:642-645
Dehydration and Electrolyte Losses in the Sport Horse - Tuffs Cummings School of Veterinarian Medicine
Kempson, S.A. 1987. Scanning electron microscope observations of hoof horn from horses with brittle feet. Vet. Rec. 120:568-570.
Kubota, J., W.R. Allaway, D.L. Carter, E.E. Cary and V.A. Lazar. 1967. Selenium in crops in the United States in relation to selenium-responsive diseases of livestock. J. Agric. Food Chem. 15:448.Lakin
Josseck, H., W. Zenker, and H. Geyer. 1995. Hoof horn abnormalities in Lipizzaner horses and the effect of dietary biotin on macroscopic aspects of hoof horn quality. Equine Vet. J. 27:175-182.
Nutrient Requirements of Horses. Sixth Revised Edition. 2007. National Research Council. Academic Press.
Schott, H. Do electrolytes really help during endurance exercise? Michigan State University College of Veterinarian Medicine website.
Van Saun, R.J. 1997. Assessing the Nutritional Status of the Horse. World Equine Vet. Review. Vol. 2:No. 4. 15 - 21.
Van Saun, R.J. 1998. Assessing the Nutritional Status of the Horse: Macronutrient Evaluation. World Equine Vet. Review. Vol. 3:No. 1. 34-39.
Williams, C. A. 2009. Herbs and nutraceuticals. In: 6th Current Therapy in Equine Medicine. (Ed. N. Edward Robinson), Elsevier Science, St. Louis, MO. pp. 87-93.
Williams, C., L. Atherly, J. Hirsch. 2007. Antioxidants and Your Horse. Rutgers University Fact Sheet #1065.
Williams, C. and E. Lamprecht. 2008. Some Commonly Fed Herbs and Other Functional Foods in Equine Nutrition: A Review. Veterinary Journal 178: 21–31.
Zenker, W., H. Hosseck, and H. Geyer. 1995. Histological and physical assessment of poor hoof horn quality in Lipizzaner horses and a trail with biotin and a placebo. Equine Vet. J. 27:183-191.