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Manganese may not be the first thing horse owners think of when they consider the minerals needed for growth and maintenance in their horses. However, this trace mineral has some important uses in skeletal and nervous system function.

The best known role of manganese for horses is its importance in bone formation. Manganese is needed in several of the steps necessary in the formation of chondroitin sulfate and in the synthesis of the organic matrix of bone, which is predominantly a mucopolysaccharide ground substance.

Manganese appears to be required in the enzymes galactotransferase and polymerase that are necessary for the synthesis of chondroitin sulfate from beta-D-glucuronide and 1,3-N-acetyl-D-galactosamine. Manganese deficiency is expressed as a disorganization of the cells making up the epiphyseal plate, a narrowing of the epiphyseal plate, and a reduction of blood vessel migration into the growth plate. Additionally, the cartilage of the growth plate in manganese-deficient animals contains lower levels of chondroitin sulfate than do the growth plates of normal animals. With respect to this function of manganese, two- and three-year-old horses in which skeletal maturation is not complete may have a slightly higher requirement for manganese than do older animals.

In its role in energy use, manganese is also known to be an activator of several enzymes such as arginase, thiaminase, carnosinase, and deoxyribonuclease. Manganese is required for oxidative phosphorylation in the mitochondria and as such is very involved in regeneration of adenosine triphosphate (ATP), a reaction critical for the maintenance of adequate concentrations of high-energy phosphagens in the athletic horse. It is unlikely that a manganese deficiency would be rate-limiting in the production of ATP, but this demonstrates the crucial role that trace minerals play as cofactors and components of various enzymes. Manganese is known to be involved in fatty acid synthesis and in amino acid metabolism, either as a co-enzyme or as an activator of enzymes. Manganese also is an effective chelating agent, allowing for more efficient and rapid transfer of amino acids.

Because of the role that manganese plays in energy transformation through lipid and carbohydrate metabolism, it is of interest in the formulation of performance horse diets. In most areas of the world, manganese deficiency does not appear to be of concern in horses grazing fresh forage. Manganese concentrations in forage range from 50-300 ppm, and these levels are adequate to meet the requirements of most horses. However, cereal grains contain less manganese and may range in manganese concentration from 5 ppm (corn) to 15 ppm (barley).

In the athletic horse on high-grain diets and consuming grass hay of variable quality, it is probable that some supplemental manganese may be required. Feeds for performance horses may be supplemented with manganese, with about one-third of the supplemental manganese coming from chelated manganese and tw-thirds from manganous oxide. High concentrations of calcium and phosphorus in feeds or forages may inhibit manganese absorption and this should be taken into account in the formulation of feeds for all classes of horses.

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