Vitamins for Horses: What Do Horses Need?

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.


What Vitamins do I need for my Horse?

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.

This article will explain vitamins for horses and what you need to focus on supplementing and what will be provided through the forage, hay, haylage or grass in the diet.

Horses on Green and Growing Grass will not need Additional Vitamins

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.

B Vitamins for Horses – What does my Horse need?

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 feed the 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.

If horses have access to plenty of fresh, green grass in the summer they will not be deficient in any vitamins.Click To Tweet

Vitamin C for horses

Vitamin C is water soluble too, but 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.

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’.

Does my Horse need Vitamin A Supplementing

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 forage 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 hay if it is under two years old.  However if you are feeding forage or feed stuffs which are not green then levels are likely to be too low.  Beet pulp and copra are low, as is straw. So if these are being used as a forage replacer then supplementation of vitamin A would be wise.  If you really need to be sure your horse has enough 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!  However do not feed carrots to horses with laminitis due to the high sugar content!

A useful article discussing vitamins for horses and just what you need to feed to match to the forage eaten.Click To Tweet

Does my Horse need Vitamin D Supplementing?

Vitamin D can be synthesized in the skin and no dietary intake is needed if the horse has exposure to sun light.  It is not known how much time is needed 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.

Both vitamin A and D 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.

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.

Vitamins for Horses – 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 Laminae Plus which is aimed towards horses prone to laminitis who maybe be eating either forage 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 Supplementing?

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.

Vitamins for Horses – Supplement Vitamin E to your Horse

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.

So our Forageplus top tip is to save money by not worrying too much about any vitamin other than vitamin E, as fat-soluble vitamins, A, D and K, as well as water-soluble vitamins C and B, are either abundant in a forage based diet or are sufficiently synthesised in the horse’s body.



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