Do you know the dangers of high iron levels in your horse’s hay or water? Iron overload is a growing concern among horse owners as more is learned about the harmful effects of having too much of this mineral in the diet.
Iron is an essential mineral that horses require to transport oxygen throughout the body. However, this highly reactive element can also contribute to oxidative damage by forming free radical molecules in the body.
When levels of iron fall out of balance in your horse’s diet, it can lead to negative effects such as inflammation, tissue damage, impaired immune function and secondary deficiencies in other vitamins and minerals.
Horses that experience iron overload may become laminitic and experience other chronic health problems. Research shows that excess iron consumption is particularly problematic for horses that have metabolic concerns such as being overweight, insulin resistance or Equine Cushing’s disease.
Iron toxicity can be caused by consuming feeds or supplements with added iron. It may also be the result of elevated levels in hay, soil or water.
Mad Barn’s AminoTrace+ Mineral and Vitamin supplement has been specifically formulated to counteract high iron forages for horses with insulin resistance or Cushing’s Disease/PPID. It contains no added iron and is made with enhanced copper and zinc levels to bring mineral ratios into correct balance.
Iron Levels in Horses
Iron (Fe) is an important micromineral for horses that is found naturally in forages, grains and water. It is a component of hemoglobin, the protein in red blood cells that carries oxygen throughout the body. It is also a component of myoglobin which stores oxygen in muscle tissue.
A 500 kg horse will have about 33 g of iron in the body. The majority of iron is found as a part of hemoglobin (60%) and myoglobin (20%). Another 20% of iron exists in storage and a small percentage (0.2%) is involved in enzyme processes.
Iron deficiency is extremely rare in horses because they typically obtain plenty of this mineral from water, feed and soil.
Anaemia (low red blood cell count) can be observed in horses, but this is usually not due to iron deficiency. Anaemia is most likely be due to blood loss, viral infections that destroy red blood cells, or chronic inflammation that prevents new red blood cells from forming.
Excess iron is a much greater concern in horses because free iron ions (Fe2+) act as oxidants causing damage to DNA, cell membranes, and other structures. High levels of iron intake have also been associated with insulin resistance and laminitis in horses.
High levels can cause liver failure, especially in young animals. Although a small amount of iron is lost in sweat during heavy exercise, in general there is no way for the body to excrete extra iron unless there is significant blood loss.
Iron tends to accumulate in tissues, particularly in the liver which acts as the main storage site. Accumulation of iron deposits called hemosiderin in the liver can lead to liver damage and metabolic problems.
Supplemental iron should not be given to horses unless recommended by a veterinarian.
Iron Intake in Horses
According to the National Research Council (NRC 2007), the iron requirement for a mature horse is 40 mg/kg of diet or 400 mg per day. This is increased to 50 mg/kg of diet or 500 mg per day for growing foals and lactating mares.
Common feedstuffs should meet these iron requirements. Forages typically contain 100-250 mg per kg of dry matter while grains contain less than 100 mg per kg of dry matter.
The maximum tolerable level of iron is 500 mg per kg of total dry matter intake. For an average horse consuming 10 kg per day, this is equivalent to 5,000 mg of iron per day.
You can submit your horse’s diet for analysis online and one of our nutritionists will be happy to provide a complementary evaluation to get a better idea of your horse’s iron intake.
Horses will also obtain this mineral from water and from soil while they are grazing or eating hay off the ground.
Iron levels in soil are correlated with clay levels. Clay based soils tend to have the highest levels of iron while limestone and sandstone have the lowest. 
Surface water generally has low iron levels (less than 10 mg per litre). Ground water can have significantly more (several mg per litre). Most municipalities offer well water testing which you can take advantage of to determine the iron content in your specific well.
Dangers of High Iron Levels in Horses
Your horse is likely easily meeting its iron requirement through their nutrition without requiring supplemental iron.
Adding iron to the equine