If you lived some before the 17th century, there is a good chance you’d be convinced that an iron (Fe) deficiency caused baldness. One of the suggested treatments at the time was consuming iron-tempered wine, produced by placing Fe filings or a rusty knife in a glass of wine. Later in the 17th century, doctors began using Fe to treat anemia. Today Fe’s role in oxygen transport is well-understood, and researchers estimate that as much as 60% of the body’s Fe can be found in blood hemoglobin (a protein in red blood cells that circulates oxygen throughout the body).

Although Fe content varies by geographic location, it remains one of the most abundant metals in soil and rock. Plant Fe content tends to reflect that of the soil, but soil type can affect the availability of soil Fe. When taking pasture samples for nutrient analysis purposes, especially if Fe is a nutrient of interest, it is important to take the samples with care. Including soil in your sample will result in an inflated Fe concentration in the final nutrient analysis report, not reflecting the true Fe concentration in your pasture.

Typically, forages contain sufficient Fe to meet a horse’s Fe requirement (recommended by the National Research Council, authors of Nutrient Requirements of Horses, 2007) of 400 milligrams per day for a 500-kilogram (1,100 pound) horse used for light exercise. Horses in more intense exercise, broodmares in late pregnancy or lactation, and growing horses have a higher Fe requirement than a horse at rest.

Overall, Fe deficiency in horses is rare, especially for those with access to pasture and hay. However, foals, similar to other young nursing animals and children, are more susceptible to Fe deficiency than adult horses due to their rapid growth rates. The foal’s digestive tract is efficient at absorbing Fe, and additional Fe supplementation in young foals should only be provided under veterinary supervision. It is thought that a true Fe deficiency or anemia in an adult horse would more likely be due to prolonged or excessive blood loss than insufficient dietary Fe intake