Cobalt is critical to the cecal and colon synthesis of vitamin B-12.
Copper is an essential portion of copper-dependent enzymes involved in the synthesis and maintenance of connective tissue,
mobilization of iron stores and of the integrity of mitochondria, melanin synthesis and detoxification of superoxide.
Foals are susceptible to copper deficiency and exhibit signs of osteochondrosis and osteodysgenesis. According to the NRC
2007, "when foals were fed a liquid milk-replacer diet containing 1.7 mg copper/kg/dm (dry matter) for 13 to 16 weeks, lameness
was observed two to six weeks after serum copper concentrations had decreased to <0.1µg/ml."
Iodine is primarily found in the thyroid gland, necessary for synthesis of thyroxine and triiodothyronine, the thyroid hormones
that regulate metabolism. It was reported that foals developed goiter when fed feedstuffs below 0.2 mg iodine/kg/dm, or with
only alfalfa hay at 0.6 mg iodine/kg/dm, and that foals returned to normal once fed 2 mg iodine/d for two to four weeks. The
requirement is thought to be 0.35 mg/kg/dm, assuming a feed intake of 2 percent of body weight.
Iron is found in hemoglobin, myoglobin, cytochromes and within a variety of enzymes, playing a significant role in oxygen
transport and cellular respiration. Iron absorption is higher with deficient rations, but decreases with excess cobalt, cadmium,
copper, manganese and zinc.
According to the NRC 2007, "the primary sign of iron deficiency is a microcytic, hypochromic anemia. Although young, milk-fed
foals are most susceptible to this anemia, iron deficiency is not a practical problem in foals if they have access to soil."
The concern for iron deficiency is especially for those foals in confinement without access to pasture soils.
Manganese is necessary for carbohydrate and lipid metabolism, and for the production of chondroitin sulfate, an important
Selenium, to be fed at 0.1 mg/kg diet dry matter, is a critical constituent of the enzymatic antioxidant glutathione peroxidase,
and along with vitamin E essential for membrane integrity and free-radical quenching.
Though a necessary nutrient, selenium toxicity occurs at levels greater than 0.5mg/kg/dm. It may be seen in horses (from regions
of the country with high selenium soil content) that exhibit "blind staggers" (blindness, colic, abdominal pain, diarrhea,
increased heart and respiratory rate) or "alkali disease" (alopecia, brittle hooves) with a chronic selenium toxicity.
Zinc, a constituent of several enzymes (e.g., alkaline phosphatase) is essential, though quite ubiquitous (in soils, galvanized/rubber
buckets). Therefore a deficiency in foals is difficult to produce, but it is characterized by poor appetite, poor growth,
skin lesions (parakeratosis, alopecia). Only 50 mg/kg dietary dry matter is required.
The trace minerals fluorine, chromium and silicon are regarded as "minerals of interest" (NRC 2007), though in each case a
definitive requirement for the horse has not been determined. Fluorine is present in most water systems and is known to be
beneficial for teeth and bone integrity.
Chromium is noted for its benefit toward carbohydrate and lipid metabolism, "especially as a potentiator of insulin to
facilitate glucose clearance," (NRC 2007).
These various minerals are necessary nutrients for growing foals, though much additional research is needed to refine their
needs. Additional information is also needed to determine if several other chemical elements may play an essential role in
trace amounts within the diet, to effect metabolism, physiology or as structural components of growing horses.
Kane is a Seattle author, researcher and consultant in animal nutrition, physiology and veterinary medicine, with a background
in horses, pets and livestock.