Horse Dietary Supplements - An Overview

Is forage enough for your horse?
Is forage enough for your horse?

Scientific research in horse nutrition over the past few decades has answered many important questions regarding the need for supplements in a horse's diet. Beyond simply contributing to your horse's good health, supplements, when used appropriately, can help prevent disease and illness as well as add vim and vigor to the horse's daily activities.

Pelletized supplements

Pelletized supplements

Easy to feed supplements are widely available. Ask your vet about supplements for your horse.

In addition to water, the five main classes of nutrients that your horse needs to survive include fats, carbohydrates, protein, vitamins and minerals. In many cases, veterinarians add electrolytes to this list, especially when the horse is athletically involved or does heavy work in conditions with high temperatures and humidity.

When your horse is lacking in any of these main classes of nutrients, supplements can fill that void to keep your horse healthy and strong. In addition, when certain diseases or conditions strike, a supplement may be the ticket to healing the disease or correcting the condition.

But, which supplements are truly necessary, and which supplements may be a waste of your time, effort, and money?

To answer these questions, think carefully about your horse's system and the way it works along with the horse's activity level and general circumstances.

The horse's digestive system

Having evolved as non-ruminant, herbivore grazers that typically spent around 18 hours a day grazing pasture grasses and other plants, horses developed a rather unique digestive system.

Equine internal anatomy

Equine internal anatomy

The horse digestive system is adapted for the diet of a continuous grazer and browser.

The horse has a very small stomach that holds between 2 and 4 gallons in the average 1,000 pound horse. Because of the small stomach, the horse's small intestine, which is 50 to 70 feet long and holds around 12 gallons, does most of the work of digesting and absorbing the nutrients in the hay and other feed the horse eats.

From the small intestines most of the liquids and roughage are then passed on to the cecum where toxic substances are detoxified and where bacteria and protozoa create fermentation helps digest most of the fiber and soluble carbohydrates and produce essential fat-soluble vitamins that are absorbed by the horse.

Keeping your horse's digestive system and work load in mind as you make decisions regarding supplements is very important.

Once the horse ingests a substance, it must go all the way through the digestive system because horses cannot regurgitate, so feeding too much of a supplement or a supplement your horse doesn't require can create problems.

In addition, a horse does not have a gallbladder, so digesting and utilizing a high fat diet is not only difficult, but is also wasteful.

What priorities do veterinarians and nutritionists recognize in the use of supplements for horses?

Many horses need only good forage, water, and a mineral block to maintain body weight and regular activity.

Editor's note

Pay close attention to ingredients and always take care when combining multiple supplements in your horse's diet. Potential interactions do exist. Play it safe, ask your veterinarian.

When hay is of poor quality or instances when a senior horse has a hard time chewing and digesting roughage, the addition of an appropriate amount of beet pulp added to the diet in small increments may be all that is needed for a good maintenance diet.

Since carbohydrates are the main energy source in most feeds, many horses do not need additional carbohydrate supplements.

So, let's take a look at the supplements veterinarians and nutritionists might recommend:


  • Proteins are made up of linked amino acids. They are the structural components of muscle and ligaments and are a source of energy. Horses need protein supplements when their diets lack essential amino acids such as lysine that are not normally synthesized in their bodies.

When choosing a supplement or a complete feed, protein is often listed first on the tag or label. Protein is an expensive ingredient and the manufacturer of the supplement or feed is required to give a minimum value of crude protein in the feed. Feedstuffs that contain more than 20 percent crude protein are considered to be protein supplements.

The quality of the protein is also important based on the amount of lysine it contains. Synthetic lysine is often added to make sure the feed has a sufficient amount of that amino acid.

Older horses, weanlings, pregnant and lactating mares, and horses with a heavy work load or high exercise level usually need a protein supplement. Ordinarily, adult horses require 8 to 10% protein in their feed.

Signs of protein deficiency include reduced growth, weight loss, loss of performance, a rough haircoat, and low milk production in the case of lactating mares.

Soybean meal with approximately 44% crude protein is the most common protein supplement. It is considered to be a high-quality source of protein with the proper ratio of dietary essential amino acids. Alfalfa hay with 17-22% crude protein is also considered to be a good source although the quality of the hay will affect the actual protein value.

Other sources of crude protein include, canola meal 40%, cottonseed meal 45%, and peanut meal 53%, although these are not as commonly used in supplements and feed for horses as soybean meal.

A number of commercial products including complete, pelleted, and sweet feeds are available that claim to incorporate a balanced nutritional source of protein for horses of different ages and activity level. In all cases, reading feed tags and contents of protein supplements is extremely important.


  • Fats are a concentrated source of energy and are necessary in the horse's diet to absorb fat-soluble vitamins and provide linoleic acid, the essential fatty acid. Although most feeds contain less than 6% fat, this amount is adequate for the nutritional needs of many horses.

Performance horses, horses with a heavy workload, pregnant and lactating mares, and under-weight horses often need fat supplements.

The most commonly used fat supplement is vegetable oil. It can be added as a top dressing to the horse's regular feed, beginning gradually with a quarter of a cup per feeding and working up to no more than two cups a day for an average size horse. (1,000 lbs.).

Rice bran is another fat supplement that is gaining popularity. Rice bran is about 20 percent fat and also supplies vitamin E and energy. Owners of performance horses use rice bran for supplementation because it helps horses maintain or gain additional weight if needed, while giving show horses a sleek and healthy appearance.

Rice bran is also palatable and easy to store and handle. Gradually adding one to two pounds to the horse's regular daily diet is usually sufficient. This amount of rice bran does not upset the balance in the horse's diet. In addition, the vitamin E is helpful in fighting the results of stress in horses that undergo strenuous exercise and changes in their environment when traveling to activities.


  • Although plenty of vitamin supplements are available on the market, vitamin supplementation is usually not necessary unless a low quality forage is being fed, the horse is involved in strenuous exercise, the horse is ill or recuperating from surgery, or is being fed a high grain diet.

Vitamin D is obtained from sunlight, so only horses that are kept in their stalls 24 hours a day need supplemental vitamin D. Vitamin E is found in fresh green forage. Vitamin K and B-complex vitamins are produced by microbes in the horse's intestines and vitamin C is found in fresh vegetables and fruits and is produced in the liver.

Severely stressed horses may benefit from B-complex and vitamin C supplements, and performance horses may need additional vitamin E.

Fat-soluble vitamins include vitamin A, D, E, and K, and water-soluble vitamins include C and the B-complex vitamins

Supplemental vitamins should be used with caution, especially the fat-soluble vitamins that include vitamin A, D, E, and K. These may reach toxic levels if over ingested because they are stored in the body if not needed immediately. Water-soluble vitamins include C and the B-complex vitamins and don't usually pose any problems because any excess vitamins are excreted in urine and through sweat.


  • Mineral supplements are often required in the horse's diet since they play a vital role in the horse's health. Although horses are able to obtain a large portion of their mineral requirements from their feed, mineral availability and concentration varies with the soil content, plant species, and stage of maturity when the feed is harvested.

Minerals are involved in maintenance of structural components including muscles, bones, and ligaments. They play roles as enzymatic cofactors and are involved in energy transfer in the horse's body. Minerals are also necessary to provide maximum absorption of vitamins, as well as adequate functioning of hormones and amino acids. Organic minerals supplied with a balanced diet help prevent muscle abnormalities, developmental orthopedic disease, and other health issues.

Generally, the major minerals of concern in supplementing a horse's feed are calcium, phosphorus, and in some geographical areas selenium. Ground limestone is a good source of calcium, and either monosodium or disodium phosphate are a good source of phosphorus. Dicalcium phosphate is the most common supplement used to provide both calcium and phosphorus.

Research has shown that calcium, zinc, copper and phosphorus benefit a horse's overall health and reduce cases of muscular problems. Trace mineral blocks are the most common way to meet trace mineral requirements. Organic minerals have been shown to have a positive effect on the immune system, development of cartilage in young horses, and healthy hooves in horses of all ages.

Horses have a natural craving for salt and an adult horse will consume about one-half pound of salt a week. Lactating mares and horses in training will consume more. If a free-choice salt block is available, most horses will consume enough to meet their needs without developing salt intoxication, if sufficient water is available.


  • Several medical studies have shown that supplementing a horse's diet with electrolytes, when appropriate, can be very beneficial, especially when the horse is hard working and subjected to strenuous exercise while competing in racing or endurance events or in cases where the horse sweats excessively.

Electrolytes come in various formulas and usually include sodium, chloride, potassium, magnesium, calcium and other minerals often mimicking the same balance as found within cell membranes. Avoid commercial formulas with added sugar and dyes.

Adding electrolytes to the feed works much better than adding them to the water, simply because the horse may not take in enough water to make the supplementation effective or may refuse to drink it if the water tastes different.

Generally, beginning electrolyte supplementation a few days before an event and continuing for a few days after the event works well to help the horse perform at the best possible level, while not suffering from the strain of the exercise. In some cases, low doses of electrolytes may be recommended on an on-going basis.

Make sure you follow the proper dosage recommendation for your horse. If the diet you are feeding is adequate and balanced, the only electrolyte supplementation you may wish to consider is sodium and chloride (salt), since sufficient potassium and other minerals are in the horse's feed.

Other available supplements: Just so you know!

In all cases, your veterinarian can help you determine what supplements will work for your horse and which supplements will be a waste of time, effort and money.

  • Senior supplements: Specially formulated for stiffness, discomfort, weight loss, poor digestion and weak immunity, these supplements may help horses as their bodies begin to function less efficiently.
  • Joint, hoof and coat supplements: Joint supplements are used to relieve stiffness and soreness, and are often used in competition horses. Key active ingredients are glucosamine, hyaluronic acid, and chondroitin sulfate considered to be excellent for sustaining healthy joints and supporting horses with joint problems, as well as relieving excessive inflammation in conditions such as osteoarthritis.

Hoof supplement formulas usually contain biotin, methionine and other ingredients essential in the production of keratin which is necessary for healthy hooves.

Ingredients for maintaining healthy coats are often combined with joint and hoof supplements and include the addition of Omega 3 and fatty acids in a flax seed base.

  • Anti-inflammatory supplements: These supplements are best used when your horse is injured, needs reduction of inflammation, or has chronic lameness issues. Some anti-inflammatories such as Bute and aspirin are best used for short periods of time, since complications can occur with longer use.
  • Digestion supplements: Horse's digestive systems are surprisingly delicate with performance horses often suffering from ulcers and other horses being hard keepers whose digestive systems lack the balance to maintain health and prevent digestive complications such as colic.

Probiotics, and prebiotics, along with amino acids claim to promote regeneration and repair of cells that line the intestines as well as help your horse's system utilize the base diet and gain full benefit of any nutritional supplements.

  • Respiratory supplements: Respiratory supplements are formulated to address chronic or seasonal respiratory problems by soothing and supporting the horse's irritated airways. Horses with allergies, heaves, stable cough and other respiratory conditions may benefit from these supplements.
  • Muscle recovery supplements: Muscle products are designed to help build up muscle protein, delay the onset of fatigue, and prevent muscle breakdown during and after heavy workouts or competitions.
  • Anhidrosis--Failure to sweat supplements: This condition is most often found with horses that live in hot, humid climates. The formulas usually include ascorbic acid, niacin, L-tyrosine and cobalt proteinate which have been found to be effective in university field tests.
  • Yeast cultures: Yeast cultures are thought to supercharge the microorganisms in the hindgut that break down fiber and reduce the build-up of acid. They may also be helpful in balancing the chemical compounds found in the horse's gut and help with the digestion and absorption of nutrients by the body. In lactating mares, the ingestion of yeast cultures helps pass on potent nutrients to foals enabling them to be healthier and grow at a better rate.
  • Herbals: Herbal products have become very popular both for people and animals. The key element in herbal treatments is supposed to be a restoration of harmony and balance in the body. Unfortunately, not all companies offer full disclosure of ingredients, fillers, strength, etc. of their herbal compounds.

In most cases, herbals are medicinal and should be administered only with the advice of a qualified health practitioner or veterinarian. Many herbs are banned by equine sport governing bodies. Be sure to check with the appropriate association before giving herbal supplements to competition horses.

  • Calming agent supplements: Formulated for the "anxious, spooky, worried" horse, these supplements claim to help the horse relax and focus on the work at hand. Formulas often include thiamine (vitamin B1) and magnesium which are essential for the stability and normal function of the cell membranes of excitable tissues such as nerve and muscle.

Other active ingredients are usually herbal and may include valerian and chamomile known for their soothing, restorative properties along with herbs such as hops, ginseng, and passion flower. Note again that some of these herbs are banned for competition horses.

Many other supplements are available in the market place. By feeding your horse a balanced diet, you can minimize the need for supplements.

Healthy treats such as carrots and apples can be part of your horse's diet, along with a little molasses, some cod liver oil, a good salt lick and when horses need it, some beet pulp that has been thoroughly soaked before feeding to add energy and protein to the diet.

Remember that not all supplements are created equal. Read labels and dosage information carefully, and always check with your veterinarian before adding supplements to your horse's diet.

About the Author

Flossie Sellers

Author picture

As an animal lover since childhood, Flossie was delighted when Mark, the CEO and developer of EquiMed asked her to join his team of contributors.

She enrolled in My Horse University at Michigan State and completed a number of courses in everything related to horse health, nutrition, diseases and conditions, medications, hoof and dental care, barn safety, and first aid.

Staying up-to-date on the latest developments in horse care and equine health is now a habit, and she enjoys sharing a wealth of information with horse owners everywhere.