Vitamins for Horses: What Do Horses Need?

Published by Sarah Braithwaite, Author & Horse Health Expert on

What vitamins do horses need in their daily diet? Learn about what vitamins are and why they are vitally important at the right levels in both summer and winter horse feeding. Understand what vitamins you need to focus on supplementing and what will be provided through the forage, hay, haylage or grass in the diet.

Vitamins for Horses What do Horses Need_

What are vitamins for horses?

Vitamins are organic compounds that are needed in very small quantities to sustain whole horse health and life.  Vitamins help the horse’s body carry out the functions essential to life such as:

Most, if not all of vitamins your horse needs should come from the grass and hay eaten every day. However if your horse is on restricted summer and spring grazing, or it is winter, or you routinely soak the hay your horse eats you will want to know which vitamins youmust supplement for horse health.

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What vitamins do I need for my horse?

Vitamins for horses can be divided into two groups fat soluble and water soluble.  You can also divide them into those you need to worry about and those you don’t.

Forageplus only stock the vitamins your horse might be deficient in if on a forage based diet. We don’t believe in adding vitamins to our supplements unless your horse truly needs them because they are not in the greatest proportion of the diet being eaten. The greatest porportion of the diet will always be grass, hay or haylage.

Horses vitamins from green and growing grass

If horses have access to plenty of fresh, green grass in the summer they will not be deficient in any vitamins. However for horses with compromised hooves there is research evidence to suggest that extra supplementation of B vitamins may be beneficial this is likely to be because stress may increase the bodies demands for the B vitamins. Horses can be stressed if they undergo a lot of physical activity or they have poor health.

B vitamins for horses

The B vitamins are water soluble, this means that where you soak your hay they will be lowered as part of the rinsing and soaking process and thrown away with the water you have soaked the hay in.  It is important then to supplement additional B vitamins to horses who eat soaked and rinsed hay as the greatest proportion of their diet.

If your horse has poor hoof quality you can add extra B vitamins although these the horse can synthesise itself. Research has shown biotin at 10 plus mg per day to be useful for improvement in hoof quality. Alfalfa however is high in biotin especially when fed fresh.  Baled alfalfa has a level of around 0.24 mg/kg

Vitamin B12 is not present in the horses diet but the bacteria living in their intestines manufacture B12 which then the horse can absorb.  No B12 deficiency in horses has ever been documented so this is another vitamin you need not worry about.  However horses on long term ulcer medications may need supplementation as research in humans has shown mal-absorption due to the action of stomach acid suppressing drugs.

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Vitamin C for horses

Vitamin C is also water soluble. Water-soluble vitamins do not stay in the body for long. The body cannot store them, and they are soon excreted in urine. Because of this, water-soluble vitamins need to be replaced more often than fat-soluble ones.

Horses can synthesise vitamin C in their bodies to prevent deficiency, but the role of dietary vitamin C is poorly understood and there is little research to suggest optimum levels.

Research does show that heavy exercise and illness can lead to low vitamin C blood levels and to maintain and support health in horses extra supplementation can be beneficial for these horses.

The NRC 2007 records that there is poor information on the levels of vitamin C in common horse feeds but research suggests that a horse on green pasture will receive 20 grams per day whilst a horse on a hay based diet will receive less than 1 gram. Horses on green and growing grass therefore will be exposed to high levels of vitamin C, perhaps the source of ‘Dr Green’.

Where you are rinsing hay to lower sugars for a laminitic horse you should not supplement extra vitamin C because it can increase iron uptake.  Many laminitics are iron overloaded so we do not advise the feeding of extra vitamin C to horses with laminitis due to this vitamin increasing the uptake of iron.

Vitamin A for my horse

Vitamin A, along with vitamin D, E and K are fat soluble vitamins. Fat-soluble vitamins are stored in the fatty tissues of the horse’s body and the liver.  These are easier to store than water-soluble vitamins, and they can in the body as reserves for days, and sometimes months. as with humans fat soluble vitamins are absorbed through the horse intestinal tract with the help of fats, or lipids.

Much fuss is made about vitamin A.  This vitamin is quite possibly the most over supplemented vitamin in the horse feed world.  Vitamin A is present in a grass, hay or haylage based diet in the form of carotenoids, primarily beta-carotene which is converted to retinol in the intestine.

Adult horses feeding on even 2 year old hay with a beta carotene level as low as 4 mg/kg (compared to 30 to 385 mg/kg normally present in forages have shown in research to have no symptoms of vitamin A deficiency.

What you need to know is that vitamin A is abundant in grass and is very unlikely to be deficient in our UK horse hay if it is under two years old.  When a food stuff is naturally green such as grass, hay, alfalfa etc. this indicates good levels of vitamin A. However if you are feeding forage or feed stuffs which are not green then levels are likely to be too low.  Levels of vitamin A in beet pulp and copra are low, as is straw. So if these are being used as a grass or hay replacer then supplementation of vitamin A would be wise.

If you really need to be sure your horse has enough vitamin A available just feed a carrot or two each day. A large carrot will contain around 8500 IU Vitamin E (as beta carotene) and the requirement for a 500 kg horse is just 15,000 IU per day so two carrots is a cheap way of supplementing vitamin A!  Do not feed carrots to horses with laminitis due to the high sugar content, it is better to use a horse feed balancer which contains good levels of vitamin A if you are feeding straw or hay which is more than one year old to laminitis prone horses or ponies.

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Learn about Laminae Plus with added vitamin A

Does a horse need vitamin D?

Vitamin D can be synthesized in the skin and no dietary intake is needed if the horse has exposure to sunlight.  It is not known how much time is needed for optimum levels of vitamin D but in humans even 20 minutes of just hands would be sufficient.  In addition vitamin D is also abundant in grass and cured hays.  Hay less than a year old contains around 2000 IU/kg , hay over a year old but under two years will contain around around 800 IU/kg.  Hay over two years old will contain around 400 IU/kg.

According to NRC (2007) figures a 500 kg horse will require 3300 IU of vitamin D per day.  An adult 500 kg horse eating 10 kg of less than one year old hay per day would be exposed to 20,000 IU. Requirements for young horses are greater but the amounts in grass, hay or haylage are still so great as to mean that supplementation is not something to worry over.  Only horses stabled out of direct sun light and not on a forage based diet or being fed feed stuffs or forage which is not green will need supplementation of vitamin A.

Toxicity of vitamin A and D in horses

At Forageplus we believe that less is more with these two vitamins and so we do not routinely add vitamin A to any of our supplements apart from the horse feed bnalancer Laminae Plus which is aimed towards horses prone to laminitis. These horses are more likely to be eating either hay, haylage or straw which is not green or be on a hay replacement diet of beet pulp and other feeds which are not green.

Both these vitamins can be harmful if supplementation is too great. The upper safe limits are reported as 16,000 IU/kg of diet for vitamin A and 44 IU/kg of bodyweight for Vitamin D.  Calculating exposure to these two minerals in feed stuffs other than reported in supplements fed is very important to maintain health and preventing poisoning.

Does my horse need vitamin K?

Vitamin K is present in plants eaten by horses and is also synthesised by bacteria in the horse’s gut in the form of menaquinone. No diet related deficiency of vitamin K has been reported in horses.  The NRC (2007) discusses that the bacterial source might not be enough to meet the needs of horses in heavy work however studies in other large animals show large bowel absorption.  The form commonly supplemented to horses however is largely useless however.

Supplementing horse vitamin E

Where your horse is on a hay or haylage diet or only has limited access to fresh green growing grass (less than 6  hours), then basically  you only need worry about vitamin E which is the number one antioxidant vitamin in the body.  A potent anti- inflammatory, it protects individual cells everyday and supplemented levels should be increased where horses are performing at high levels or are sick.  More information about vitamin E and levels can be found in our Forageplus Talk article on this vitamin.

Summary of horse vitamins needed

Tips for health horse feeding in winter

Understand horse electrolytes  –  what should you feed – when should you feed

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