What Supplements Do Your Horses Really Need Each Day


Your horses need a range of minerals but they must be in correct proportions. The actual quantities are important but so is the balance of the formula, more is not better, so the safe way to supplement is to use a correctly balanced formula from a reputable manufacturer, added to a balanced diet of Fibre, Carbohydrate, Protein and Fat.

This applies whether they are at rest, in light work or performance horses. The harder the work the higher the amounts they need, breeding horses, competition or racing are all working hard.

Horses in work also need electrolytes, horses with very little green feed will need Vitamin E but no other supplementation of vitamins is required for a horse in normal conditions whether resting or in work. It is necessary to check out the labels of the products you are feeding, all supplements should show the level of active ingredients, and it should be easy to work out the exact amount of each per dose. View products that do not have details on the label with caution – would you eat something that you didn’t know what was really in it?

What Minerals do Horses Need

These are divided into two definitions: Macro and Micro,

The actual amounts are important to know but also the ratios between them, too much of one can inhibit the uptake of another.

So, for an average 500 Kg horse the standards are: *

MACRO Maintenance Performance
Calcium 20g 40g
Chloride 46g 93g
Magnesium 9g 15g
Phosphorus 14g 29g
Potassium 28g 53g
Sodium 14g 41g
Sulphur 15g 18.8g
MICRO Maintenance Performance
Cobalt 0.5mg 0.6mg
Copper 100mg 125mg
Iodine 3.5mg 
Iron 400mg 500mg
Manganese 400mg 500mg
Selenium 1mg 1.25mg
Zinc 400mg 500mg

*From National Research Council Nutrient Requirements of Horses.

Note that while some of these are provided for in pasture – but no pasture in New Zealand will provide all the minerals needed in the levels needed by a horse.

So how do you work out what to feed, – well the simple answer is to cover the daily need rather than having to calculate what is or isn’t already available to them, and that is by using a fully balanced formula that has been calculated for New Zealand conditions with correct ratios of the minerals. Allowances should have been made in the mix for normally available levels (standard pasture and feed) and increasing the dose will allow for poor conditions or harder work.

Ratios  – The Relationship of Different Minerals

The most well-known ratio is that of Calcium to Phosphorus, it is important that the calcium level is higher than Phosphorus, ideally 1.5 or 2:1. If the Calcium intake is less than Phosphorus intake, the uptake of Calcium may be impaired.

High Calcium from supplementing just Calcium, can create ulcers – osteochondritis is a possibility if the Calcium is high and the Phosphorus not increased, imbalances in that ratio have been linked to OCD.

Copper and Zinc are linked, too much Zinc (ideally 1:3) but if over 6 times the Copper, it will inhibit the uptake of Copper, a very important mineral especially for young horses. A formula of minerals will often have higher levels of copper than needed to make sure that a correct ratio is maintained as Zinc can be readily available from pasture, even bore water.

High levels of Iron can interfere with Copper and Zinc uptake. It is unnecessary to supplement iron as so much is provided from normal feeds, for example hay is high in Iron. It is well known that Iron should never be in the same mix as Vitamin E, the presence of Iron will prevent any uptake of Vitamin E. If a feed or formula has this combination then it should shed doubt on the validity of the formula.

Calcium should be higher, at least 2:1 or more to Magnesium. There is a tendency to overfeed Magnesium in the misguided belief that it will calm the horse (the Magnesium Myth). Low Magnesium can be linked to nervousness or anxiety (although there are many other options that will create this see Thiamine B1), but once the required level is made available to the horse –it can only excrete it if magnesium oxide is given, that’s the inorganic magnesium, organic or chelated is not water soluble and so it cannot utilise the excess. So, feeding a high level will not result in higher levels of calmness – it is not a sedative. Too high a level will cause imbalance in the cells of the horse and that is a negative effect on health, excessive can be toxic.

Toxicity in Horses – Unsafe Mineral Levels

Incorrect levels of some minerals may develop into toxic states of the horse. The most well-known is Selenium. Many areas of New Zealand have low Selenium soils and therefore it is necessary to supplement, this must only be done after a blood test has been taken and assessed by a veterinarian. Maintenance of the small amount needed for horses in normal conditions with normal blood levels, can be achieved by a formula that contains Selenium Selenite (an inorganic form), this will not create a high blood level. A horse that is too low will need Selenium to be administered over and above a standard mineral formula. Ideally an organic (or chelated) powder form is the safest way to supplement, a small amount daily. There is an option of liquid Selenium but this is very concentrated and a tiny amount is needed, sometimes only fortnightly, and it can easily be over dosed. High levels of Selenium from over supplementing will have very adverse effects on the health of the horse and has proved fatal.

Excess Iron, especially in young animals, can be toxic and sometimes even fatal in foals. Some Iron supplements have been implicated in chronic iron toxicity (in mature animals) when fed in the form of ferrous sulphate. There is no such thing as low haemoglobin levels from low dietary intake, the cause needs to be assessed from other aspects, even the ability of the horse to utilise the Iron that is available. Also, there is no scientific data that shows that extra supplementation with iron does improve red blood cell, haemoglobin concentration or packed cell volume.

Iodine is another mineral that can be toxic if in excess, only a small amount is required daily and this is usually provided correctly in most mineral mixes. However, if feeding a kelp product, it is very important to know the source and the Iodine levels of the kelp that has been used. The correct kelp is called Ascophyllum nodosum from the North Atlantic – this is low in Iodine. A horse needs 3.5-4.5 mg per day, it can tolerate up to 50 mg before serious negative health issues occur. Some kelp products from normal seaweed will provide 120 mg per day so check the label, or the website carefully.

Excess Phosphorus may cause skeletal abnormalities. It can occur where horses are fed large amounts of grain based feedstuffs and are not supplemented with a mineral mix with Calcium, or are grazing on pasture (or hay) with high oxalates such as kikuyu or white clover.

Vitamins – What Does Your Horse Really Need?

As mentioned under normal conditions it is not necessary to supplement Vitamins, some are actually synthesised within the horse. There are a few exceptions for supplementing and a few negative issues from over supplementation. Horses that are constantly stabled with limited sunlight, minimal forage and horses with chronic conditions and illness may need some vitamins to offset those unnatural situations.

One exception is for Vitamin E, a shortfall of this vitamin can occur: when a horse has a low intake of pasture, or the pasture is particularly poor quality, they are kept stabled horses and are not being given green feed such as fresh Lucerne chaff – a good source of this vitamin. Note poor storage of fodder will also reduce the availability of Vitamin E. It is often recommended, in conjunction with selenium, for horses prone to tying up. As mentioned above it is pointless providing Vitamin E in conjunction with Iron. The current recommended daily dietary intake of Vitamin E for adult horses is 500-1000 IU, excessive Vitamin E may result in decreased Vitamin A absorption. Two types of Vitamin E are available – synthetic and natural, it has been promoted that natural Vitamin E is better as it has a higher biological activity, but it has a very high cost. In animals other than horses, the size of the dose can be substantially reduced with natural Vitamin E therefore offsetting the cost, however, in horses this does not apply and the cost is very high. It is more economic to give a higher synthetic Vitamin E dose. Synthetic Vitamin E will still provide the daily requirement and optimum levels in the plasma.

Vitamins A and D – are fat soluble and are stored by the horse, they rarely need to be given to the horse, indeed dietary excesses can be very negative, just 10 times the requirement for Vitamin D may be toxic. The differential between low and a toxic level of Vitamin A is relatively small. The only time Vitamin D may be needed is when a horse is stabled without access to good light, nor being ridden outside.

Vitamin C – horses will synthesise sufficient for their needs. Horses in period of high stress may benefit from supplementing but again excess is negative and should be discontinued when conditions are normal.

Other exception is B Vitamins – thiamine (B1), riboflavin (B2), Niacin (B3), biotin (B7), folacin (B9), pantothenic acid (B5), pyridoxine (B6) and cobalamin B12 are all synthesised in adequate quantities within the gut. However again periods of high stress, prolonged travel, sudden hard work, high gran intake etc may reduce the efficacy of the natural process and so a short-term supplement of B1, B2, B3, B6 and B12 will assist the horse during that period until his own gut is back to normal.

Thiamine B1 in particular can be lowered by work demand and a low level will result in a spooky distracted horse, it can be safely supplemented as it is water soluble and any excess will be excreted.

Biotin has been found to improve quality hoof growth when supplemented at 15 mg per day.

Vitamin K is also synthesised by the horse and supplementation is unnecessary.

Electrolytes – When do Horses Need Them

Again, balance is the key and a correctly formulated mix is vital to the horse in work, especially in conditions that cause sweat. Replacement of all salts lost in sweat is essential to the health of the horse. Just salt (sodium chloride) is not enough and too much salt is not good either. It has been proven that horses do not self select the amount of salts need so relying on a salt block is not effective. For more on electrolytes read our article ‘‘Electrolytes – Why, When, What, How‘.


The solution to understanding supplements and their labels is to analyse the conditions that your horse lives in, close to normal good pasture or a combination of stable and a balanced feed and some pasture, or extreme e.g. stabled on high grain, only poor pasture, large amounts of hay etc.

Normal conditions are assisted by a correctly formulated mineral mix with macro and trace minerals. Poor or unusual conditions will need analysing to see what may be deficient, but keep in mind that correct ratios are so important therefore it is not advantageous to quickly add a single mineral or a vitamin. Even a horse in imbalanced conditions will benefit from the addition of a good fully formulated mineral mix which should offset any shortfalls not provided for in the pasture, hay or feed, plus the addition of say Vitamin E for example, or a little Vitamin D if no light is available, rebalancing the constituents of the feed itself may also assist the horse to maximum health.

At Vetpro the welfare of the horse comes first (not the market) so we strive to provide supplements with just what the horse needs based on scientific data. We also hope to help horse owners with information on aspects of nutrition and horse care, check out the rest of our website for more articles or contact us by email :

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