Free Choice Minerals for Horses

The following is an excerpt from an article entitled, Holistic Equine Nutrition written by Dr. Joyce Harman, of Harmany Equine Clinic, based in Virginia. 


Mineral balance is perhaps even more critical than vitamin balance in a horse’s diet. There is a complex interaction between many minerals; even a slight excess of one mineral in a diet can mean another mineral may not be absorbed. Trace minerals are a catalyst to help break major minerals down into a form that can be utilized.

In nature each “weed” has a trace mineral associated with it, so if a particular mineral is needed the horse will often eat the weed if it is non-toxic. Also, if the soil needs a particular mineral a certain weed will grow there to help provide that mineral. Soils that are or have been used to grow crops are depleted of trace minerals, so the grains grown on these soils and fed to horses are depleted. Additional mineral supplementation becomes extremely important.

Horses will naturally select from free-choice minerals as long as they are not too sick to sense their needs (perhaps through recognition of the energetic frequency of the minerals.) Conventional nutrition research reports that no species can accurately select free-choice minerals. However, upon observation it becomes apparent that the seasonal variations in mineral and vitamin consumption are significant.

For example, in the flood-stricken mid-west in the late 1990s, the horses ate large quantities of B vitamins during the summer, when they would normally get all the B vitamins they needed from pasture. When coats change in the spring and fall, horses eat extra sulphur, which is used in the manufacture of hair (sulfur-containing amino acids). In the spring when the grass is growing rapidly and is low in magnesium, the horses consume may consume extra free choice magnesium, but not at other times of the year.

Free-choice minerals need to be fed with the salt provided separately. If both are fed together in the standard mineralized salt block, the salt will limit the mineral intake. The mineralized block is composed of about 94% salt. A salt block, whether mineralized or plain, is really designed for use by cows with their rough tongues and horses with smooth tongues often have a difficult time getting enough, especially when that is the only way they can obtain minerals. If the horses need minerals and not salt, they will not eat the mineralized block any more than a person would eat an over-salted dish of food.

When horses are given plain minerals the quantity they eat is often astounding for a few weeks to months until they have balanced out their minerals. Then the amount consumed tapers off to a maintenance level. However, for successful free choice eating, artificial flavorings and molasses should not be used as they may affect the intake of the nutrient. Molasses-based blocks will be over eaten due to the desirable flavor.

One of the least understood minerals is calcium. Calcium is often given in excess to “help build strong bones”. Calcium is also present in high levels in alfalfa hay, a horseman’s favorite hay, and yet some people want to add more calcium to a diet high in alfalfa. Calcium is a key mineral, however much of the time when a “calcium” deficiency problem is detected, the real problem may be the level of available phosphorous.

Phosphorous is an expensive mineral, so it is more likely to be deficient in a supplement. Calcium is cheap and can also be used as a processing agent in soybean meal to improve the “flowability.” The calcium used as a processing agent does not need to be included in the stated ration formula and if it were, the cost of the phosphorous to balance it could be enormous. When phosphorous is added to the diet, calcium becomes more available to the body.

Anybody can balance for deficiencies by adding something, but it takes a lot of technical skill and money to balance excesses; all the other ingredients must be added to bring the levels up to balance the one that is in excess. For example wheat bran is often fed in excess; it is too high in available phosphorus and is made from wheat, which can act as an appetite depressant if fed in large amounts. Steps can be taken to tie up excesses but few are successful. Clay can sometimes help by tying up everything in the gut; then the bacteria can slowly take what they need and the rest can pass out in the manure.

Very few companies provide a plain mineral supplement; usually salt will be in the top half of the ingredient list. Avoid unbalanced single minerals or combinations of just a few minerals unless they are offered as a part of an extensive free-choice system (and are palatable for that purpose). Many products are formulated based on human requirements, which may not work with the nutritional needs of the horse.

Race horses and many anemic horses are constantly given iron to “build their blood,” when most horses, even those with anemia, have plenty of iron in their bodies. Excess iron in the intestines can tie up calcium. Racehorses have more bone problems than any other group of horses, so the last thing they need is a calcium imbalance.

Minerals occur in nature in all forms (acetates, citrates, sulfates, etc.), and are best if fed in many different forms. Chelated minerals are popular in some circles, and can be one form of mineral provided but should not be the only form. Chelation is when the mineral is bound to another nutrient in a complex molecule. Some forms of minerals are poorly absorbed, particularly calcium carbonate, though with the correct supporting minerals and enzymes, some is absorbed.

As long ago as the early 1900’s, a study was done showing that silica and calcium fed together provided stronger and more flexible bones. This study was done on chickens and it has been primarily the chicken industry that had used the information. But bones are bones, and cattlemen are now using silica for their herds, though possibly as a filler, rather than for its true nutritional value. Horses desperately need stronger, more flexible bones, but the horse world has not caught on to the silica idea. Diatomaceous earth is an excellent source of silica (68%), as well as calcium and magnesium. And yes, horses will eat diatomaceous earth in a free-choice format.

Water frequently has excesses of a particular mineral or ingredient such as nitrates that can affect vitamin A and selenium absorption. Without vitamin A the body cannot use vitamin D, E or the full B complex vitamins correctly. Toxic levels of nitrates cause ammonia build-up in the fermentation vat of the cecum which can lower hemoglobin in blood, creating anemia.

High iron in the water has an indirect effect on calcium and phosphorous. This occurs because phosphorous is the closest to iron in atomic weight; high iron impedes the utilization of phosphorous, which in turn affects the availability of calcium. However, it is not a calcium deficiency; it is a phosphorus and iron problem. Sometimes the mineral content of water is seen as a precipitate (white, green or other colored deposit); if this type of precipitation is occurring in the gut, valuable minerals are being lost directly into the manure.

The ideal source of minerals is the single-molecule minerals found tied to carbon in the long-stem fiber of the plants. The plant has done all the work and left the mineral in a form available to the body. These minerals can be found in truly naturally healthy pastures. A future article will cover natural ways to improve soil and pasture health.

Until your pastures are capable of providing complete minerals, the best way to approach mineral nutrition is through a free-choice system, with the salt and mineral separated, using as large a selection as your management will allow, either just salt and minerals separately, or a larger selection. Also to complete.

If your horse is boarded in a pasture, or you only visit a few days a week, it is very easy to offer the minerals just on the days you are there. Horses will eat minerals when they need them, and they do not have to have them available all the time.


To read this article in full, please click here.


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

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6 Responses

  1. Julie says:

    Is there a list of examples for extensive free choice mineral feeding?

    • Casie says:

      Hi Julie–do you mean the different free-choice products which are available?

      • Julie says:

        Not so much the product (although those are welcome too).

        In the article it says: “Avoid unbalanced single minerals or combinations of just a few minerals unless they are offered as a part of an extensive free-choice system (and are palatable for that purpose).”

        So I am wondering, if you make an extensive free-choice system for the horses – which minerals (or maybe examples of products) can be fed?

        • Casie says:

          That’s can be a tricky question, Julie. It depends on what’s lacking in your specific pasture or hay. (I get my hay tested so I know what’s lacking.) The most common deficiencies are copper, zinc, and sometimes phosphorous. Occasionally calcium and pretty much never iron. Also, salt always needs to be available as there’s not enough in grass or hay. Advanced Biological Concepts (ABC) has some good free-choice minerals. Pricey, but good.

  2. Cyndi says:

    Hi Casie, I’m curious…If my hay is lacking in Phosphorous, magnesium, zinc and copper would you suggest it is best to just put out buckets of these four minerals along with salt and let the horses decide which and how much of each they want to eat?

    • Casie says:

      Hi Cyndi–I think that might be a good idea to try. I know ABC (Advanced Biological Concepts) sells the individual minerals which you could use for that.

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