Balanced Equine Nutrition

Mineral Ratios and Deficiencies/Excesses

Our goal is to ensure that our horses are provided a diet containing nutrient levels which meet or exceed the NRC’s minimum requirements for horses while at the same time maintaining the minerals in correct ratios to one another. 

Minerals are classified into two primary groups: major and minor (or trace). The major minerals consist of calcium (Ca), magnesium (Mg), phosphorus (P), sodium (Na), and potassium (K). The trace minerals consist of copper (Cu), zinc (Zn), iron (Fe), manganese (Mn), selenium (Se), and iodine (I).

Mineral ratios are important to the horse because minerals interact and they compete with one another for absorption in the horse; too much of one interferes with the absorption of other minerals. The figure below illustrates the diverse and complex nature of the interactions amongst minerals.

mineral relationships and interactions: calcium, iron, manganese, zinc, phosphorus, magnesium, copper

If a mineral has an arrow pointing to another mineral, it means a deficiency of that mineral or interference with its metabolism may be caused by excesses of the mineral from whence the arrow originates.

Adapted from "Trace Elements, Hair Analysis, and Nutrition."

Using three minerals, calcium, magnesium, and iron, let us take a simple example of how a popular commercial equine supplement that is labeled for use with grass and mixed grass hays fairs with an average "mixed mostly grass" hay1.

The optimal ratio of calcium and magnesium falls in the range of 1.5 - 2 to 1, but let us take 2 to 1 for simplicity, i.e. for every 10 grams of calcium in the diet, there should be 5 grams of magnesium.

Calcium (Ca)

Magnesium (Mg)

Ca to Mg ratio

Mostly Mixed Grass Hay
15 lbs

48 grams

15 grams


Popular Supplement,
label dose

7.5 grams

0.7 grams


Hay + Supplement

55.5 grams

15.7 grams


From the table above, we can see that the supplement makes the ratio worse, increasing it from 3.2 to 3.5, instead of improving it (decreasing it from 3.2 which is what we want). The hay has ample calcium, but not enough magnesium, but the supplement provides a high amount of calcium and very little magnesium.

The NRC recommends 272 mg of iron for a 1200 lb horse at maintainence. Hays range considerably in their iron level, but most hays contain iron far in excess of what is required by the horse. The typical hay in this example provides 4200 mg of iron which is more than 15 times higher than what is required by the horse. This popular supplement, however, supplies an additional 550 mg of iron which further increases the imbalance.

Not only do many commercial supplements fall short of truly balancing and optimizing your horse's diet, they worsen imbalances already present in the diet. An excess of one nutrient is just as bad as a deficiency; balance is the key. A forage test along with a customized supplement provides your horse with exactly what he needs and nothing that he doesn't.

External effects of mineral imbalances

This hoof photo is from a horse who began a properly balanced diet; no other changes were made. Note that the numerous surface cracks began to grow out upon starting the balanced diet.

effect of mineral and diet imbalances on hoof quality

1 mostly mixed grass hay data from Dairy One's database of accumulated samples 5/01/2000 through 4/30/2005.

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