Vitamins & Minerals for Horses

Vitamins & Minerals for Horses

Last month I wrote about protein and how the quality of the protein is more important than the % of protein in the diet. If you purchase a feed that lists that it is 14% protein but it is a poor quality protein, your horse is likely to become protein deficient. Quality matters and nothing matters more than the quality of protein in your horse’s diet. What role do vitamins and minerals play in a horse’s diet, and how do you know how much your horse needs?

What do we really know about vitamin and mineral needs for horses?

Your veterinarian or an equine nutrition consultant recommend you get a vitamin and mineral supplement for your horse so you do an online search to take a look at your choices. You end up slogging through several pages of choices, each supplement promising a highly palatable, bioavailable supplement that will meet all of your horse's basic nutrition needs. How do you choose? How do you know which vitamin supplement is the best for your horse? 

There’s a pretty good chance that not even your veterinarian can give you good guidance. The truth is that we know very little about what horses need when it comes to vitamins and minerals. I’d like to take this opportunity to just go through some of the basics of vitamins and minerals so you, the horse owner, can understand what they do for a body so you can make a better decision for your pocketbook and for your horse.

Vitamin vs Mineral

A vitamin is an organic, carbon based compound that is necessary for normal growth and metabolism. Vitamins are required in small quantities in the diet because they cannot be synthesized or produced by the horse. Vitamins have diverse jobs when it comes to keeping your horse's body functioning. For example, vitamin D aids in absorption of calcium from your horse's small intestine, while vitamin E scavenges for free radicals that can damage the body's cell membranes.

A mineral is an inorganic, non-carbon based, substance that is stable at room temperature and has an ordered arrangement of atoms. Almost 5,000 minerals are known to exist, but a relatively small number are required to make sure your horses body functions the way it should. Some, but not all, minerals are critical in your horses diet.

What do horses need?

Most recommendations for the equine diet are based on estimates published by the National Research Council of the National Academies. This information comes from a literature review performed by experts on their panel. It's important to realize that these requirements aren't necessarily determined by specific studies. The most recent estimates were published by the NRC in 2007. The most difficult thing to decide is whether your horse needs supplementation at all. If you have a healthy horse in moderate work and he/she has turn-out and a diet with adequate-quality hay, chances are his vitamin and mineral needs are met already. If you are concerned or your horse has limited access to pasture or good quality hay, the following information might be helpful.

Vitamin Guide

Vitamins can be divided into two groups: fat-soluble and water-soluble. The fat-soluble vitamins include A, D, E, and K, while water-soluble vitamins include vitamin C and the B vitamin group: thiamin or B1, riboflavin, B12, niacin, folacin, pantothenic acid, biotin, and B6.


Vitamin A

Vitamin A is important for proper muscle function, ocular (visual) health, and helps keep mucous membranes healthy. It's also involved with reproductive function and assists in the metabolization of keratin for strong, healthy hoof horn.

Where does vitamin A come from?

Many commercial feeds provide Vitamin A in the ration. However, the Vitamin A they add is likely from an animal source so your horse will only be able to utilize about 8% of the total amount. Beta-carotene, which comes from plant sources, is converted into vitamin A by your horse. What the horse does not immediately need will be stored in his liver, which will help protect him from deficiency for several months when pasture is no longer available or hay quality suffers.

How much does a 1,100-pound horse need?

Approximately 15,000 IU per day (1mg of B-carotene is equal to approximately 400 IU of vitamin A). Vitamin A supplementation is rarely necessary unless your horse has limited access to fresh, green forage. If you have fertility problems with your mare or if she's pregnant but lacks access to pasture or good, green hay, vitamin A supplementation might be recommended.


B Vitamins

B vitamins are involved with metabolism of carbohydrates, proteins, and fats. These vitamins help your horse produce the energy from the food he eats.

Where do B Vitamins come from?

B vitamins are produced by the bacteria that live in your horse's large intestine. They're also found in good-quality pasture and hay. Most, if not all, of your horse's B vitamin needs are met by production in his own body, and the remaining amount he needs is usually met from hay or pasture. Specific levels for supplementation haven't been established. If a horse has poor-quality hooves, supplementation with 20mg per day of biotin may help. Pair this with a good quality protein that provides your horse with the amino acids, lysine, threonine and methionine to improve absorption.


Vitamin C

This vitamin scavenges free radicals from the body to help protect them from damage. Vitamin C also supports the formation of collagen, an important connective tissue in the body.

Where does C come from?

Vitamin C is synthesized from glucose by your horse's liver. Vitamin C requirements for horses are unknown at this time.


Vitamin D

Vitamin D assists with absorption of calcium from your horse's small intestine and helps regulate excretion of phosphorus. These functions are critical for maintaining health of bones and joints.

Where does D come from?

Vitamin D is produced by your horse's body when he's exposed to sunlight (UV radiation). If he grazes outside for 6 to 8 hours per day, he'll likely meet his needs for this vitamin. Small amounts of Vitamin D are also present in hay, although amounts will decrease over time.

How much does a 1,100-pound horse need?

Approximately 3,000 IU per day. Exercise can increase needs for vitamin D, so hard-working horses who are not kept outside may require supplementation.

Fresh green grass is the best source of Vitamin E. Sainfoin and alfalfa hay are higher in E than other hay sources, although levels of Vitamin E decrease with storage over time. If you are going to supplement with Vitamin E, D-alpha-tocopheral is the most active form of this vitamin.


Vitamin E

Vitamin E scavenges the body for free radicals and protects the exterior of the cells. This is critical to support proper immune function. Vitamin E also supports nerve and muscle function. Vitamin E works in concert with selenium to make sure muscles function properly. Veterinarians often prescribe Vitamin E with Selenium for horses with Lymes or EPM to provide support to the cells in the central nervous system.

Where does E come from?

Fresh green grass is the best source of Vitamin E. Sainfoin and alfalfa hay are higher in E than other hay sources, although levels of Vitamin E decrease with storage over time. If you are going to supplement with Vitamin E, D-alpha-tocopheral is the most active form of this vitamin.

How much does a 1,100-pound horse need?

Minimums are not established but approximately 500 IU per day is recommended. If your horse has no pasture turnout, you’ll likely need to provide a Vitamin E supplement. Hard-working athletes, horses fed high-fat diets, or pregnant mares may benefit from additional Vitamin E.


Vitamin K

Vitamin K is crucial for proper function of your horse's blood-clotting mechanisms. It is also increasingly recognized as important for maintenance of bone health.

Where does K come from?

Vitamin K is present in hay and is produced by the normal bacteria in your horse's large intestine.

How much does a 1,100-pound horse need?

Horses produce adequate amounts of Vitamin K so the average horse needs no supplementation. However, if your horse has prolonged gastrointestinal problems his ability to produce adequate Vitamin K could be compromised so you may want to consider Vitamin K supplementation.


The majority of your horse's mineral needs are met with pasture and hay. However, the ratio between two particular minerals is as important as the actual amount available, because one might influence absorption or activity of another. For example, calcium:phosphorus ratios should be maintained at 1.5:1 or higher because phosphorus has a negative effect on calcium absorption. Likewise, zinc to copper ratios should be 1:3 because these two minerals compete for the same transport mechanisms in the body. Another important factor that's gaining attention from nutritionists is the form of minerals provided in the ration. Mineral salts (inorganic) are believed to be much less easily absorbed by the horse than their organic counterparts when paired with amino acids. The following is a short list that tells you a bit about the most important minerals that should be considered in your horse's ration.

Horses have what is known as “nutritional wisdom” when it comes to his salt needs so if a salt block is available, horses generally consume what they need.


Sodium Chloride ie salt

Salt helps maintain proper fluid balance in your horse's body. Your horse gets sodium chloride from his basic diet and most concentrate rations contain some salt.How much does a 1,100-pound horse need?

Horses have what is known as “nutritional wisdom” when it comes to his salt needs so if a salt block is available, horses generally consume what they need.

When does a horse need more?

If your horse works hard, especially in hot conditions, it's especially important to have sodium chloride available to replenish what is lost.



Critical for building bone.

Where does Calcium come from?

Calcium levels are high in alfalfa hay, where Ca:Phos ratios are often as high as 6:1. Calcium is also present in grass hay but the ratios can be closer to 1:1, making grass hay somewhat calcium-deficient.

How much does a 1,100-pound horse need?

A 1,100 pound horse will need 30g to 40g per day..

When does a horse need more?

Calcium is critical during growth and development of bone, both during gestation and after birth. If your horse is fed a diet of grass hay and cereal grains it's likely that his Ca:Phos ratio is less than 1.5:1, and extra calcium would be advised.



Works in combination with calcium to give strength to bone.

Where does Phosphorus come from?

Phosphorus is present in most hays and cereal grains. Brans are very high in phosphorus.

How much does a 1,100-pound horse need?

A 1,100 pound horse will need 18g to 29g per day.

When does a horse need more?

As with calcium, phosphorus is most important during growth and development. Senior horses may also be less effective at absorbing phosphorus so a senior feed with a slightly higher amount of this mineral might be advised.



It plays a role in energy metabolism, muscle contraction, and nerve impulses. It is also one of the major minerals represented in bone.

Where does Magnesium come from?

Magnesium is present in most hays and grains.

How much does a 1,100-pound horse need?

A 1,100 pound horse will need 7.5g to 12g per day. 

When does a horse need more?

Magnesium is commonly used as a calming supplement, with the belief that a subtle deficiency of this mineral could cause nerve excitation, and that extra magnesium helps relax muscles.



Maintains electrical balance across cell membranes and plays an important role in muscle contraction and nerve impulses.

Where does Potassium come from?

Potassium is found in relatively high amounts in most hays.

How much does a 1,100-pound horse need?

A 1,100 pound horse will need 25g to 32g per day.

When does a horse need more?

Potassium is lost in sweat. A hard-working horse might require supplementation along with other electrolytes, particularly if working when or where the temperatures are high. *For horses with the genetic muscle disease known as HYPP care should be taken to minimize potassium in the diet.



Plays a role in bone and joint development. Copper is also involved in formation of hemoglobin, the molecule that carries oxygen in your horse's bloodstream. Without enough copper a horse may become anemic.

Where does Copper come from?

Copper can be found in most hays, beet pulp, chia, and flax seed. Molasses is a very good source of copper and is commonly used in commercial concentrate rations.

How much does a 1,100-pound horse need?

A 1,100 pound horse will need 0.1g to 0.12g per day.

When does a horse need more?

Molybdenum and zinc may interfere with copper metabolism, and excessive iron can interfere with copper absorption. If these minerals are known to be present in high amounts, extra copper might be advised. This can be especially important for growing youngsters, because of the role copper plays in bone and joint development. If your horse's coat gets sun bleached and turns orange in the summer, it's possible he's lacking copper in his diet. 



Assists a wide range of enzymes with their functions. It is also involved in immunity, wound healing and can play a role in reproductive function.

Where does Zinc come from?

Most pastures, hays, and grains contain zinc in adequate levels.

How much does a 1,100-pound horse need?

A 1,100 pound horse will need 0g to 0.5g per day.

When does a horse need more?

Iron can interfere with zinc absorption so if your horse is exposed to excess iron, additional zinc may be required in his diet. As with copper, a lack of zinc may contribute to your horse's coat turning orange in the sun.



It is important for many different cell mechanisms. Most important are its roles in muscle and nerve function. Selenium is essential for proper metabolism of vitamin E.

How much does a 1,100-pound horse need?

A 1,100 pound horse will need 3mg per day. Where does Selenium come from: Selenium is found in the soil and in hay grown on that soil. Some areas of the country have large amounts of selenium in the soil, while others are deficient. When does a horse need more? Some areas of the country (Pacific Northwest, the Great Lakes, and the eastern seaboard) are selenium-deficient so selenium supplementation is required. Of all the minerals, the range between deficiency and toxicity of selenium is fairly narrow so this mineral should be considered carefully. A simple blood test can tell you whether your horse has adequate selenium in his diet, and can help guide proper supplementation. When in doubt, seek the advice of an equine nutritionist.     

~ From the desk of Mary Hartman, CEO and Founder

*This is a personal blog. Any information herein is not to be construed as medical advice.