The Importance of Mineral Balance in Your Horse’s Diet

A common question I get from readers and friends is ‘How much ______ (insert mineral here) should I feed my horse?”  I wish I had a simple answer for that, but the truth is that I don’t.  There is no one-size-fits-all approach to supplementing minerals to horses and that’s because of several factors.  It depends on:

1.) How much of each mineral your horse is currently consuming in his diet, and

2.) Your horse’s specific needs according to size, age, physiological state (pregnant, lactating, etc.), and work load.

Fortunately, you can find your horse’s specific nutrient needs (including minerals) using the National Research Council’s (NRC) guidelines.   But in order to know how much of each mineral your horse is currently getting, you’ll need a forage analysis.  If you feed a concentrate, you’ll need to look at the guaranteed analysis of this as well.

Even if a specific mineral is known to be deficient, something every horse owner needs to understand is this:  you can supplement a mineral as much as you want, but if it’s not fed in the correct ratio along with certain other minerals (either trace or major minerals), it’s basically a crapshoot.  The mineral ratios and mineral balance in your horse’s diet are very important.

Weighing Magnesium

Major Minerals

The major minerals are deemed ‘major’ because they are needed in greater amounts (in grams) when compared to the trace minerals.  For your horse, the ones you should be most concerned with are these:

  • calcium
  • phosphorus
  • magnesium
  • potassium
  • sodium
  • chloride

After determining your horse’s needs for each major mineral, you then need to consider two important ratios–the calcium to phosphorus ratio and the calcium to magnesium ratio.

Calcium to Phosphorus Ratio

According to the NRC, the calcium to phosphorus ratio should be somewhere between   1.1: 1 to 2.5: 1.    That means, the horse needs more calcium than phosphorus  (roughly one-and-a-half times to twice as much.)  My past hay analyses showed to be particularly low in phosphorus (until we fertilized), so I supplemented large amounts of phosphorus at times.

I’ve since learned that adult horses can tolerate a calcium to phosphorus ratio up to 6:1 as long as their phosphorus needs are met, so I’ve stopped supplementing it.  Plus, I wrote an article on a study about phosphorus losses in horses for The Horse earlier this year which confirmed my suspicions that phosphorus doesn’t always need to be supplemented.  However, if you have young, growing horses, I would shoot for the NRC recommended ratio.  Phosphorus is very important in bone development.

Calcium to Magnesium Ratio

Perhaps of greater importance for the adult horse is the calcium to magnesium ratio.  I say this because so many horses’ diets tend to be deficient in magnesium, often with noticeable effects.  (See this post on supplementing magnesium for more information.)  The calcium to magnesium ratio should also roughly be 2: 1 as well.  (1.5: 1 to 2: 1 is okay.) I stick to the 2: 1 ratio at all times though.

With grass hay or pasture as my horses’ primary source of nutrition, I’ve never had to supplement calcium.  I have, however, had to regularly supplement magnesium (up to 10-15 grams).

Trace Minerals

The trace minerals are of no less importance in the horse’s diet; they are simply needed in lesser amounts (in milligrams).  The trace minerals you should be most concerned about for your horse are these:

  • iron
  • copper
  • zinc
  • selenium
  • manganese
  • cobalt
  • iodine

One trace mineral that you will probably NEVER need to supplement is iron.  Horses get plenty of iron in their diet as it is.  Copper and zinc are very commonly deficient in horses’ diets.  Selenium and iodine may be as well.

Iron: Copper: Zinc: Manganese Ratio

For the average horse, Dr. Kellon recommends a ratio in the range of 4: 1: 3: 4 to 10: 1: 3: 3 (iron to copper to zinc to manganese).  That means there should be anywhere from four to ten times as much iron as copper and three times more zinc and manganese than copper.  You will want to balance your minerals to the iron or manganese, whichever is a greater amount on your analysis.

For overweight, insulin resistant, or other metabolically challenged horses, you will want to stick the 4: 1: 3: 3 ratio though.  This is because iron can be even more of a problem for these horses.  (see this post for more information on iron overload.)  Since you can’t lower the amount of iron already in the diet, this means you will have to increase your copper and zinc (and possibly manganese) amounts to meet this ratio.


I know all this can be confusing.  I’m not a math-inclined person myself, but I’ve learned to balance these ratios using my forage analyses.  If you don’t want to balance the minerals yourself, I would recommend working with an equine nutritionist or feeding a commercial mineral supplement with high levels of copper and zinc and  NO iron in it.  California Trace is a good one.

But next time you’re considering supplementing a specific mineral, consider the ratios–they’re very important!




Hi! My name is Casie Bazay. I'm a mom, a freelance writer, and a certified equine acupressure practitioner.

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4 Responses

  1. Jessica says:

    What about areas where well water is very high in calcium how do you handle something like that with no way to really measure? We do have a lot of minerals in our well water as well.

    • then5925 says:

      Hi Jessica,

      Have you had a water analysis done? There is a way to factor in minerals from water. I can e-mail a fact sheet to you if you’d like. If you know you’re dealing with high calcium and you have no way of measuring though, I would still supplement the magnesium–at about 10-15 grams. This should be safe for a full-sized horse.

  2. What effect does not having ratio of 2 to 1 of calcium& Magnesium in horses diet? Thanks Jim

    • Casie says:

      Hi James–Horses don’t usually have an issue with getting enough calcium–it’s magnesium that can sometimes be a problem (in my experience). A magnesium deficiency can affect the horse’s nervous system, bones, and muscles, among other things. Magnesium deficiencies have also been linked with insulin resistance, and when supplemented magnesium, these horses tend to improve.

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