Molybdenum (Mo) isn’t usually a topic of conversation around the tack room, but this mineral is an important part of your horse’s diet. It is component of biological enzymes involved in the metabolism of purines, which help make up some of the building blocks of deoxyribonucleic acid and ribonucleic acid (better known as DNA and RNA, respectively).

Requirements and Sources

It’s unclear exactly how much Mo a horse needs in his diet. Most horse feeds contain an estimated 0.3 – 8 milligrams per kilogram of dry matter. Concentrations in plants or pasture growing on shale, granite, or marine-origin soils, or soils which have been contaminated by industrial pollution, could be notably higher (the latter over 200 mg/kg dry matter) (Lewis 1996, NRC 2005). Sandy soils, however, are low in Mo.

While specific values were not reported, the National Research Council’s Nutrient Requirements of Horses (NRC) reports that research found grass forage generally had higher Mo concentrations than legumes.

Deficiency and Excess

Neither Mo deficiency nor toxicity has been reported in horses. In birds and other mammals, a Mo deficiency can result in reduced growth rates