Iron in the Equine Diet

cases, however, this amount may be much higher because of soil contamination in the forages our horses eat. It’s not unusual to see iron analysis on hay samples between 200 to 500 mg per kg of dry matter (of the forage). Some of this iron will be part of the grass plant, but a substantial proportion of it will be from the soil contamination inherent in stored forages for horses. Soil is loaded with iron, and despite our best efforts, horses inadvertently consume it. Even horses on pasture will be consuming some soil, but the good news is that much of the iron in soils is not available for absorption in the small intestine of a horse. If the iron consumed cannot be broken down to the absorbable form Fe2+ in the acidic environment of the stomach, it will pass through the digestive tract of the horse and into the manure.

Iron in Forages or Feeds Like Beet Pulp

The iron inherent in grass plants, such as pasture or hay, could be from either digestible or indigestible iron sources. Plants use iron in photosynthesis and store iron as a substance called phytoferritin. This stored iron is usually, but not always, available for uptake in the small intestine. The digestibility of iron in plants is a function of the maturity and fibre content of the plant.

Fermentation of the forage fibre in the hindgut will release any iron associated with it, but iron cannot be readily absorbed by the horse once it passes from the small intestine. Beet pulp is an excellent example of this. An analysis of beet pulp will show that it often contains high iron levels, 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 horse’s 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.