Iron in the Equine Diet

this horses have an excellent ability to regulate the uptake of iron in the gut. The more iron in the diet the less they actually absorb. Research in horses has established that on average only 20 percent of the iron they consume is actually available. A great deal of the iron they consume is not digestible and will be excreted in the manure
Main Sources of Iron in the Horses Diet
The typical equine diet will provide at least 100 mg of iron per kg of dry matter daily. That means that our 500 kg horse eating 2 percent of its body weight in dry food per day 10 kg will consume at least 100 mg x 10 kg 1000 mg of iron per day. In many cases however this amount may be much higher because of soil contamination in the forages our horses eat. Its 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