Iron in the Equine Diet

but two factors significantly reduce its potential impact on the iron status of the horse. Firstly the iron in beet pulp is largely in a form unavailable to horses and therefore will pass through the gut into the manure. Secondly beet pulp is loaded with a hindgut fermented complex carbohydrate called pectin. The iron in beet pulp tends to be associated with these complex carbohydrates and will only have the potential to become free iron once the beet pulp has undergone fermentation in the hindgut. Because the horses gut absorbs iron primarily in the small intestine the chance of free iron in the hindgut being absorbed is greatly reduced if not entirely eliminated.
Commercial Mineral Supplements
Iron coming from your mineral supplements and manufactured feeds will have varying availability depending on the source. Iron oxide is completely unavailable to the horse while iron sulphate may be more available depending on other factors in the equine diet. Many equine mineral supplements utilize dicalcium phosphate DCP often referred to as Dical as both a calcium source and a phosphorous source. Along with calcium and phosphorous DCP carries about 1000 mgkg parts per million or ppm of iron as an inherent part of the rock it came from. Manufacturers often call this iron background noise as it is present but was never part of the formulation of the mineral supplement. Most equine supplement manufacturers include this iron on the product tag as part of total iron. If you are trying to source a low iron mineral the background noise iron might be a source of alarm however there is no research that demonstrates that the iron present as a contaminant in dicalcium phosphate is at all available to horses.
There are mineral products available that have been formulated to be VERY low in total iron. These supplements will be using a phosphorous source other than DCP. Be sure to check the tag of any products claiming to be very low in iron as they may also be low in calcium depending on the phosphorous source used. A low calcium mineral is not necessarily a bad thing for a horse getting calcium from something like alfalfa hay but if you have a performance horse or in particular a growing horse you should consult with a qualified equine nutritionist or your veterinarian as to whether the mineral is suitable for your horse.