The difference between organic and inorganic mineral compounds lies in the chemical structure of the molecules. The atoms of a mineral are always bound to one or more other atoms to form a stable compound, which can then be given to your horse in powder or liquid form. This bond with other atoms determines whether the mineral is in an organic or inorganic form.

Organic Mineral Compounds

In an organic compound, minerals are bound to carbon-containing molecules, such as amino acids or proteins. An example is zinc methionine, where zinc is bound to the amino acid methionine. Magnesium chelate is another example of an organic compound.

Inorganic Mineral Compounds

In an inorganic compound, minerals are bound to inorganic molecules, such as sulfates, oxides, or chlorides. An example is magnesium oxide, where magnesium is bound to oxygen.

Biological Availability

Whether a mineral (or another nutrient) actually reaches the place where it is used in the horse’s body depends on its biological availability. This biological availability is determined by how well it is absorbed from the digestive tract into the bloodstream. For most minerals, this absorption process is the limiting factor—what happens during the transfer from the intestines to the blood. The digestibility of a supplement often determines how well it is absorbed and utilized in the cells.

Horses Are Different

The absorption of minerals in horses is often different (and less efficient) compared to other mammals. This is partly because horses carry out a large part of digestion in the hindgut (the large intestine and cecum) with the help of microorganisms. Additionally, factors such as old age, poor teeth, pregnancy, lactation, work, and sweating can significantly increase a horse’s mineral requirements.

For example, a horse loses relatively more minerals through sweat than a human does. When humans adapt to heat and physical activity, our sweat becomes less salty, helping us retain minerals in our blood. Horses, however, continue to sweat out minerals regardless. This is why electrolytes are often recommended in hot weather and for horses that perform intense work.

Organic or Inorganic?

Which type of minerals should you use in a horse supplement? To answer that question, it is important to consider the following:

• Organic minerals are often more easily absorbed by the horse’s body, meaning less is wasted and the minerals are used more efficiently.
• Inorganic minerals are usually cheaper and more readily available, but their absorption may be lower.
• In general, organic mineral compounds contain fewer mineral atoms than inorganic compounds such as carbonates, chlorides, and phosphates.
• In some cases, different minerals are absorbed through the same pathway and may compete with each other. This applies, for example, to copper and zinc, as well as calcium and magnesium. To compensate for a deficiency, it may be beneficial to "hide" the mineral in an organic compound. These are often absorbed via a different mechanism and do not compete for the same pathway.

Calcium and Magnesium

Horses do not always absorb minerals efficiently and sometimes require large amounts, especially if they are in work, are older, or have a foal at foot. Research has been conducted on the absorption of certain minerals in horses.

Calcium is generally well absorbed, particularly in the form of calcium carbonate and calcium chloride. Organic calcium is more bioavailable than inorganic calcium. Horses mainly obtain calcium from roughage such as grass and alfalfa, as these contain water-soluble forms of calcium. Calcium is primarily absorbed in the small intestine. Not just the amount of calcium, but especially the calcium-to-phosphorus ratio in roughage determines whether a horse gets enough calcium, as these minerals share the same absorption pathway. Magnesium is also absorbed via this route and may be affected if the diet contains high levels of calcium. The ideal ratio between these three minerals is 2:1:1 (calcium : phosphorus : magnesium).

Another important fact: Phytate/phytic acid from wheat can limit calcium absorption, which is one of the reasons why feeding large amounts of grain to horses is often discouraged. Magnesium is well absorbed in chelate and sulfate form. Magnesium oxide is less bioavailable but much cheaper. It is often recommended to feed a combination of organic and inorganic minerals to benefit from the advantages of both. Additionally, consulting a veterinarian or equine nutritionist is advisable to ensure a balanced diet for your horse.