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Horse grazing short grassYour 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: *

MACROMaintenancePerformance
Calcium20g40g
Chloride46g93g
Magnesium9g15g
Phosphorus14g29g
Potassium28g53g
Sodium14g41g
Sulphur15g18.8g
MICROMaintenancePerformance
Cobalt0.5mg0.6mg
Copper100mg125mg
Iodine25.mg4.4mg
Iron400mg500mg
Manganese400mg500mg
Selenium1mg1.25mg
Zinc400mg500mg

*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