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Vitamins, or so-called, micro nutrients, are of vital importance on all levels of health and wellbeing, both physically and mentally, for our horses. For without the right levels and balance of these nutrients our horses can suffer serious physical, metabolic, fertility and mental health problems once they are out of balance.

Some vitamins are synthesised by bacteria in the horses small or large intestine or in the liver.

Most compound feeds have been fortified with a good balance of vitamins, and minerals, so it should not be necessary to add extra supplements. It also has a drawback; most feeds won’t give the exact iu by volume, so you can never be quite sure how much is in the feed. The problem occurs when feeds are being fed without concern for the breed, the work or the sex of the horse, the age and whether the horse is mostly in or outdoors. All these considerations can have far reaching effects as to what vitamins or minerals a horse actually needs. In other words, each horse is an individual with individual needs and requirements.

It is vital that horses get good green herbage, and if you have pasture, it is a good idea to plant out herbs, herb mixes specifically for horses can be bought from most good seed providers. Herbs have long roots so are ideal for absorption of minerals from the soil, providing the soil is not depleted.

You can have your soil tested to see as to what mineral content it has, if the soil is poor in minerals, it may be advisable to give your horse supplements, especially if it outdoors most of the time and mostly feeds on poor quality pasture. Good mineral uptake is vital for health and growth in foals and young horses. And in breed mares and stallions, as many aid reproduction and fertility.

A note of caution: you can overdose a horse on vitamins and minerals, which can cause toxicity problems. If you are unsure of what your horse needs and what diet to feed your horse seek advise from a qualified equine nutritionist. This is also important when you have horses in sport performance, elderly horses, young horses or horses with whom you want to breed.

Vitamins are either fat soluble and stored in the liver or water soluble, these are not stored but pass through the gut.



Vit A – Retinol

This vitamin specifically boosts the immune system, and for foals/young horses it promotes the growth of healthy bones and tissue. It also improves night vision.

Good Vit A sources can be found in leafy greens, high quality hay and carrots.

For horses prone to laminitis avoid feeding carrots, as they are high in sugar. Also found in cod liver oil, although some may not want to feed their horse animal derived supplements.

Deficiency signs show in the horse in skin disorders, diarrhoea, poor growth, decreased appetite, loss of condition and they may become more susceptible to respiratory infections.

You do need to be careful with adding vit A as a supplement, as it is stored in the liver, and a good store can see a horse through for several months. An excess of this vitamin can cause toxic build-up.

Vitamin D – Calciferol.

This vitamin is absorbed into the skin by sunlight, as in humans. It is needed for the metabolism of fat and acts as an anti-oxidant. It is also necessary in the absorption of calcium and phosphorus in the gut. In winter time, when sun light levels are low, even for outdoor horses, it is advised to add Vit D as a supplement, it is found in cod liver oil, but if you are against feeding animal derivative to your horse you can find vit D as a powder supplement.

Not getting enough vit D may result in lameness, skeletal defects in foals and young horses specifically and swollen joints.

As with vit A, too much of this vitamin can lead to soft tissue ossification, this may lead to pain and immobility on the site of the ossification. It may raise the blood calcium levels which in turn may cause deposition in the blood vessels, joints and heart tissue.

Vitamin E – Tocopherol – Especially necessary for health in fertility

This is a vitamin which has several important functions, it needs selenium (a mineral which we will discuss in part two.) to be properly absorbed as it aids in the utilisation of oxygen and it aids in metabolism of fats which in turn improves performance and stamina, especially needed in horses who work hard and sports horses, as it also improves muscle development. It also aids in fertility health. Breeding mares and stallions are given extra vit E in the beginning of the breeding season. The condition Azoturia (tying up) may be relieved with this vitamin. This vitamin also reduces nervousness and is often used for race horses who are high in energy due to their condition and high carbs feeds for energy.

Good sources are to be found in Linseed oil, alfalfa, green feeds, barley, rye and other grains.

Deficient intake can result in liver damage if there is not enough selenium present for absorption. It may also cause degenerative muscle tissue, defects in red blood cells, infertility and low performance.

Vitamin K – Menaquinone

Necessary for the metabolic uptake of cellulose and blood clotting.

The bacteria from Green leafy foods make this vitamin in the large intestine.

Unless your horse has to use anti-coagulant drugs, which would interfere with the effectiveness of this vitamin, horses are not usually deficient in this vitamin.

But as this vitamin is stored in the liver, caution is advisable to use this vitamin as a supplement. 



This regulates metabolism of carbohydrates, fats and in particular glucose. This vitamin is synthesised in the large intestine by bacteria.

Unless your horse eats bracken, which contains a B1 antagonist, there is rarely a deficiency seen.

Nonetheless deficiency can lead to, loss of condition and impaired growth.

B2 – Lactoflavin or Riboflavin

This is an important vitamin for heart tissue health and the nervous system, and can help in making the horse more quiet and less restless. It also aids in the metabolism of fats, carbohydrates and protein.

Grass, herbage and dried yeast are good sources and it is synthesised by bacteria in the large intestine. Deficiency will result in poor growth and condition and will lower the energy levels.

B3 – Nicotine acid/niacin

Aids fats, protein and carbohydrates metabolism and promotes healthy skin.

Cereals (barley, wheat) provide a good source and is synthesised by bacteria in the large intestine.

B5 – Pantothenic Acid

This vitamin is synthesised by bacteria in the large intestine and controls metabolism of fats, carbohydrates and protein. It isn’t common for horses to be deficient in this vitamin but shows up as poor growth and condition.


B6 – Pyridoxine

This vitamin influences some 50 different enzymes, so is one of the more important soluble vitamins for your horse. It aids metabolism of fats, carbohydrates and protein. It is found in good quality grass, herbage and green forage. Deficiencies are rare, but will occur when your horse does not get enough grass and dried or fresh herbage, it may then affect growth and skin and blood changes.

B12- Cyanocobalamin

An aid for the metabolism of proteins, fats and carbohydrates. It aids the reproductive process and specifically necessary for the utilisation of protein which in turn promotes healthy growth, it also improves appetite, and helps in the formation of red blood cells. Useful for older horses who may have less appetite and sick horses who may have gone off their food due to their low condition. 

The mineral Cobalt, (see part two), is necessary to aid production of bacteria which synthesises this vitamin in the large intestine. When deficient, which is not that common, you may see it reflected in poor coat health, slow growth, and infertility. Anaemia may also occur, although more so in younger rather than mature horses.


This is a constituent of Cartlidge cells (joints) it is also involved in the transmission of nerves and cell structure maintenance and helps in transportation of fat in the body. It can be synthesised from amino acid methionine (plant proteins). Deficiency is not common as it can be found in most feed stuffs.


Folic Acid – Folacin

Vital in red blood cell production and necessary in the prevention of anaemia.

It is synthesised in the large intestine from green forage and herbage and good quality grass. When there is a deficiency, it will be noticed in poor growth, anaemia and inefficient performance.


Specifically necessary for good hoof health and healthy skin, it also helps to metabolise protein, carbohydrates and fat. When there is not enough Biotin in the feed, such as soya, yeast, maize and green forage, it will show in poor hoof wall health and skin problems.

Vitamin C – Ascorbic Acid

Aids in the utilisation of Iron, so will help in the recovery of anaemia. It helps with good energy levels and strengthens the body’s defence system against disease. Also helps prevent nosebleeds. It can help to reduce stress and skin problems. It is synthesised in the liver from dietary glucose. Deficiency is rare, but will show itself in poor health of skin and poor performance due to stress.


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Geertje is an Equine Nutritionist and Behaviour Consultant covering Oxfordshire and Berkshire

Please note that this article contains general advice, however, as each equine has their own individual needs, it is always advised that you consult an independant Equine Nutritionist.


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