Iron (Fe) is essential for your horse to be able to transport oxygen throughout his blood. It makes up the center of hemoglobin, which is the oxygen transport molecule in blood.
It is also present in myoglobin, which helps get oxygen into your horse's muscles.
60-80% of the mineral in your horse's body is found in hemoglobin and myoglobin. Another 20% is stored in the liver, spleen, and other tissues, and the rest is distributed throughout the body in various places.
To lesser degrees it is also a part of muscle tissues, as part of myosin and actomyosin (both help muscles to move), and is also a part of some enzymes.
Absorption rates are very low, usually somewhere around 15% or less, depending on how old the horse is (young foals absorb it better than older horses) and how much of the mineral is in the diet (when more is present in the diet, a lower percentage is absorbed).
Feedstuffs in the average equine diet vary widely in the concentration of this mineral that they contain.
Most forages and by-products contain somewhere around 100-250 mg/kg dry matter.
On the other hand, most grains contain less than 100 mg/kg dry matter.
However, some concentrates contain anywhere from 500-1400 mg/kg dry matter!
A deficiency is not a concern for the majority of horses, especially if they have access to soil.
If a deficiency were to occur, it would result in anemia. Young foals are more susceptible to anemia than grown horses, though again, it is of little concern since most horses obtain enough of this important mineral.
Excess Fe in the horse diet will not usually cause visible changes except in cases of very severe toxicity.
However, it will decrease the level of zinc in the blood and liver.
Due to the fact that the symptoms of toxicity do not show on the outside, it is suggested that large doses of supplemental Fe not be given to horses, unless there is a very specific reason to believe that the diet is deficient.
In fact, supplemental Fe can be fatal to newborn foals! In the late 1980's products containing ferrous fumurate designed to be administed to young foals were removed from the market, and since then the incidences of toxicity have decreased.
Iron is an essential mineral for the transport of oxygen throughout the body, and as such, it is essential that horses receive enough every day.
However, that is easily accomplished through the average horse's diet, so except in specific deficiency cases it is suggested that Fe supplements not be given due to the adverse effects outweighing the possible benefits.
Likewise, this mineral should never be supplemented to foals, as it is toxic to them.