Manganese (Mn) plays a vital role in metabolizing carbohydrates and fats, as well as in the synthesizing chondroitin sulfate, essential for cartilage formation. It is part of superoxide dismutase, an antioxidant which helps mitigate damage caused by free radicals.

Requirements and Sources

The National Research Council’s Nutrient Requirements of Horses (NRC 2007) indicates that a mature 1,100-pound (500-kilogram) horse requires a minimum of 400-500 milligrams of Mn per day. Forage and unrefined grains are the main natural sources of Mn for horses and other livestock; the NRC estimates that most forages contain a range of 40-140 milligrams Mn per kilogram of dry matter, which, even on the low end, should be sufficient for most horses. Grains, such as oats and barley, typically contain less Mn than forages.

In some areas, water sources can contain substantial amounts of Mn, which can affect dietary need. But, the only way to know what minerals are in your horse’s water is to have samples analyzed.

Deficiency and Excess

Little is known about Mn deficiency in horses. In ruminants, swine, and poultry, a deficiency can result in abnormal cartilage development, enlarged joints, crooked limbs, and reproductive problems. A link between Mn deficiency and limb abnormalities has been suggested, but not proven, in horses.

There are no known reports of Mn toxicity, however too much Mn in the diet can interfere with the proper absorption of phosphorous, a macromineral, is necessary for proper bone growth and bone health.

Take-Home Message

As with all minerals, balance is key. Although only a relatively small amount of Mn is required in the horse’s diet, too much can interfere with absorption of other important minerals. In most cases good-quality forages, with or without a commercial grain concentrate, should provide sufficient dietary Mn. An equine nutritionist can help you determine if your horse’s diet contains a proper balance of minerals.