Nutritional supplements in horses

What should practitioners consider when evaluating and recommending nutrient supplements for equine patients? In addition to looking at the traditional issues of an animal's age, activity level and general health, practitioners should also consider the nutrient's perceived benefits, efficacy and bioavailability.

Following is a look at nutritional supplements, including nutraceuticals, how they are and aren't regulated and the purported benefits of some of the supplements.

First, the basics

The Nutrient Requirements of Horses from the National Academy of Sciences is the basis for evaluating nutrient needs of horses.1 Published in 2007, it provides a thorough review of the various classes of nutrients (e.g., energy, carbohydrates, protein and amino acids, fats and fatty acids, vitamins, minerals), including estimates of nutrient requirements for growth, maintenance, reproduction and performance. It also discusses water and water quality, feeds and feed processing, feed additives, feed analysis, ration formulation and evaluation and the nutritional needs of horses experiencing various disease states.

When feeding horses, management conditions are pivotal; environmental access to nutrients can influence the feeding management that's implemented. Horses that live outdoors with access to pasture are fed very differently from those in confinement.

In addition to the nutritional requirements responsible for sustaining normal physiology, nutrient expenditures associated with degrees of activity can influence feeding practices. Horses may be involved in high levels of performance (e.g., racing, polo, dressage, cutting and roping, ranch and farm work), as well as moderate levels of exercise. Horses at varying levels of exercise require different amounts of energy, as well as other nutrients such as electrolytes and water for intense physical activity and performance.1 Special considerations are also given to young and growing horses, breeding stallions and pregnant or lactating mares.

Horses may be fed fresh and stored forages; grain mixtures; processed grains compressed by rolling, flaking or crimping; pelleted grain mixtures; pelleted forage; textured feeds and extruded feeds (cubes, wafers, pellets). Rations are usually composed of ingredients that are processed after harvesting. Processing can affect the physical, chemical and microbiological properties of the feedstuff by altering the size, density, nutrient content and texture. Digestibility, utilization, intake and acceptance may also be affected.

Nutrient supplements defined

The Federal Food, Drug and Cosmetic Act [Title 21, Code of Federal Regulations §321(f)] defines feed additives and includes items that are intended or reasonably expected to become either directly or indirectly a constituent of food or that may alter the characteristics of a food. Additives also include substances intended for use in the manufacturing, processing, packaging and storage of a food. Animal diet feed additives may be non-nutritive ingredients that stimulate growth or other aspects of production, improve the efficiency of food utilization or benefit the animal's health or metabolism.

Numerous nutrient supplement compositions are available. Such supplements are often mixtures of vitamins and minerals, though some include ingredients not commonly part of the natural equine diet. These supplements may include botanicals, herbs, extracts, enzymes, metabolites and amino acids. They're sold in the form of tablets, liquids, pastes, powders and granules.

The American Association of Equine Practitioners (AAEP) endorses the 1996 American Veterinary Medical Association (AVMA) guidelines,2 including the use of nutraceuticals. The therapeutic use of micronutrients, macronutrients and other oral nutritional substances is permitted, though veterinarians should be aware of the ingredient content and their benefits, bioavailability, efficacy and safety.

While not applicable to animals, a dietary supplement is defined by the Dietary Supplement Health and Education Act (DSHEA) as one that "contains one or more of the following dietary ingredients: vitamin, mineral, herb, or other botanical, amino acid or dietary substance for use by man to supplement the diet by increasing the total dietary intake, or a concentrate, metabolite, constituent, extract, or combinations of these ingredients."3 Under DSHEA, dietary supplement manufacturers are responsible for ensuring a supplement is safe before it's marketed and providing a reasonable assurance that no ingredient presents a significant or unreasonable risk of illness or injury.

Manufacturers cannot claim their products prevent, treat or cure disease. Within the DSHEA, though limited in its ability to regulate products prior to marketing, the Food and Drug Administration (FDA) is responsible for taking action against any unsafe dietary supplement product after it reaches the market. Generally, manufacturers are not required to register their products with the FDA nor get the FDA's approval before producing or selling dietary supplements. Manufacturers must ensure product label information is truthful and not misleading. Unlike for human dietary supplements, the Center for Veterinary Medicine (CVM) has determined DSHEA doesn't apply to animals, animal feeds or to veterinary nutraceuticals.4,5

Animal dietary supplements

According to the National Research Council, an animal dietary supplement is defined as "a substance for oral consumption by horses, dogs and cats, whether in or on feed or offered separately, intended for specific benefit to the animal by means other than provision of nutrients recognized as essential or for provision of essential nutrients for intended effect on the animal beyond normal nutritional needs, but not including legally defined drugs."6

Nutrients and nutrient supplements are regulated by various agencies including the FDA's CVM and the individual states where the products are sold. Guidance for the state agencies is provided by the Association of American Feed Control Officials (AAFCO).5 AAFCO writes and revises model bills, which include food and drug regulations set forth in the Code of Federal Regulations and are often the basis of state feed regulations. The AAFCO official publication, published yearly, includes continuous revisions and additions to approved ingredients and animal feed additives. Recently, AAFCO took further action regarding nutraceuticals, establishing the Enforcement Strategy for Marketed Ingredients, which addresses unapproved ingredients and ingredients with unapproved claims.5

Some manufacturers have introduced animal products from their position within the human nutraceutical market. Many of these products have emerged in the horse market via a bridge from the human supplement market with the assumption that all species need the supplement sometimes without scientific data supporting its efficacy, bioavailability and nutritional purpose in horses. Equine practitioners should scrutinize those products before recommending their use in horses.

The National Animal Supplement Council (NASC), formed in 2001, is a nonprofit industry group consisting of manufacturers, suppliers, veterinarians, dealers and animal owners dedicated to protecting and enhancing the health of horses and companion animals. The group's aim is to place safety standards on animal supplements and on the manufacturers and to promote the use of safe ingredients in their products. The NASC Quality Seal Program is awarded to those manufacturers that meet the organization's standards (for more information, visit www.nasc.cc).

However, NASC does not require companies to perform efficacy studies on their products or verify that scientific research data are available proving the products are effective for the benefit(s) they claim in horses.

Note, numerous reputable nutrient supplement companies are not members of NASC but do follow proper labeling and legitimate good manufacturing practices and have their products supported with scientific data showing their benefit and efficacy for use in horses.

Nutraceuticals defined, examined

A veterinary nutraceutical is defined by the North American Veterinary Nutraceutical Council (NAVNC) as "a substance which is produced in a purified or extracted form and administered orally to patients to provide agents required for normal body structure and function and administered with the intent of improving the health and well-being of animals."7 NAVNC's mission is to promote and enhance the quality, safety and long-term effectiveness of nutraceutical use in veterinary care.

Feedstuffs have nutritive value and are generally recognized as safe, but nutraceuticals may not necessarily be. Nutraceuticals include selected nutrients, dietary supplements, functional foods, genetically engineered designer foods, hyper-nutritious foods, pharmafoods, phytochemicals (including herbs) and processed foods.

Various herbal and botanical nutraceuticals are marketed by equine supplement manufacturers for multiple purposes. Here is a brief synopsis of some of these items, their purported benefits and their noted application in horses. Although included in the list of horse products, some of these nutraceuticals have been scientifically proven only for laboratory animals or people. Regardless of the manufacturer's common claims, most of these are not AAFCO-approved feed ingredients, nor are they supported by research for use in horses.

• Boswellia serrata: Safe use in pregnant mares hasn't been established, so it should be of concern for breeding mares. It may be a GI irritant.

• Methylsulfonylmethane (MSM) is used to treat various illnesses in horses, including chronic muscle soreness, epiphysitis, acute laminitis, pleuritis, recurring digestive tract disorder and arthritis. While no data exist for its effectiveness, and it's intended as a source of bioavailable sulfur, studies evaluating its potential chondroprotective effect in horses haven't been reported.

• Beta-hydroxy beta-methylbutyrate (HMB): Although HMB is used as a supplement to increase performance; prevent muscle damage after strenuous effort; increase strength, endurance, and lean muscle mass and prevent exertional rhabdomyolysis, there are little or no data to support its use in horses.

• Devil's claw (Harpagophytum procumbens) is purported as a natural anti-inflammatory and analgesic for providing pain relief to horses and reducing inflammation in equine joints, but there are no supportive data in horses. It is contraindicated in horses with gastric and duodenal ulcers.

• Cat's claw (Uncaria tomentosa): No studies are believed to have been performed in horses, but cat's claw purportedly fights viral infections and toxins and inhibits microorganism growth.

• Valerian (Valeriana species): Its composition includes valerenic acids (monoterpenes, sesquiterpenes) and iridoid glycosides. Several positive benefits are claimed for horses for its sedative or tranquilizing properties because of its effects on suppressing gamma-aminobutyric acid, but no known studies have been done in horses. Valerian should not be used in conjunction with central nervous system depressants or before a horse is anesthetized.

• Ginseng (Panax species) is commonly studied for its immunostimulatory properties. It's been shown to exert an inhibitory effect on IL-1b and IL-6 gene expression; decrease TNF-α production by macrophages; decrease COX-2 expression and suppress histamine and leukotriene release in mice and rats. As an equine supplement, ginseng is purported for stimulating the immune system, decreasing stress and increasing optimal performance, but there's no scientific literature to support its use in horses.

• Fenugreek (Trigonella foenum-graecum) is noted as a digestive tonic, but it should not be used during pregnancy. Moreover, there is no data to support its use in horses.

Most of these nutraceuticals are not AAFCO-approved feed ingredients. No scientific literature exists that shows nutritional or other benefits in horses or supports their use in horses. Other substances in need of data to support their use in horses are outlined in Table 1.

Some of these ingredients should be prescribed with precautions. For example, some may be associated with adverse reactions to their active ingredients. Some may cause undesirable side effects or may produce effects when given with prescribed drugs. Some herbs should be of concern if fed to pregnant mares since they may stimulate the uterus (e.g., liquorice root, oregano, sage, vervain, fenugreek). Milk thistle may interfere with uptake of P450 drugs. And marshmallow root shouldn't be used simultaneously with drugs absorbed into the intestine, since it may decrease uptake.

Ed Kane, PhD, is a researcher and consultant in animal nutrition. He is an author and editor on nutrition, physiology and veterinary medicine with a background in horses, pets and livestock. Kane is based in Seattle.

REFERENCES

1. National Research Council. The nutrient requirements of horses. 6th rev. ed. Washington, DC: National Academy of Sciences Press, 2007.

2. Guidelines for alternative and complementary veterinary medicine. J Am Vet Med Assoc 1996;209(6):1027.

3. The Dietary Supplement Health and Education Act. Congressional Rec 140:1994.

4. AAFCO Official Publication. Oxford, Ind: Association of American Feed Control Officials, 2007.

5. AAFCO Enforcement Strategy for Marketed Ingredients Working Group. AAFCO. Available at: http://www.aafco.org.

6. National Research Council. Safety of dietary supplements for horses, dogs, and cats. Washington, DC: National Academy of Sciences Press, 2009.

7. North American Veterinary Nutraceutical Council. Nutraceutical Council. J Equine Vet Sci 1996;16(11):486.