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 Cushingâ€™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 diet is strongly discouraged unless recommended by a veterinarian. This might be the case if your horse has experienced blood loss which might occur due to injury, bleeding ulcers, chronic inflammation or a heavy worm load. These cases should be evaluated by a veterinarian to determine if adding more of this mineral to the diet would be appropriate.
Below is a list of the top 5 reasons to minimize iron exposure for horses:
- Oxidative damage â€“ Free iron ions are highly reactive and damage lipids (fats) in cells creating more free radicals. This sets off a vicious cycle of free radical damage that can lead to cell death which prevents tissues from functioning normally.
- Insulin resistance â€“ Although the mechanisms are not clear, high iron levels have been linked to equine metabolic syndrome. This correlation has also been seen in other animals including humans.
- Absorption of other minerals â€“ High levels can decrease zinc and copper absorption from the diet which may lead to a secondary deficiency. Equine nutritionists try to maintain the ratio of these three minerals at 4:3:1 of iron to zinc to copper to avoid interference with each other.
- Immune function â€“ High levels of iron in blood suppresses immune function. The ability for antibodies and immune cells to fight infections is decreased and the ability to create new immune cells is also impaired. 
- Laminitis â€“ Elevated iron can cause laminitis and other hoof problems. This could be related to insulin resistance or due to poor absorption of other minerals that are important for hoof health.
When there is too much of this mineral in your horse’s body for a long period of time, it can contribute to a wide range of secondary problems. Excess iron puts additional strain on the body’s natural antioxidant defense systems.
Antioxidant nutrients like selenium, Vitamin E and Vitamin C may become depleted in your horse at a faster rate, resulting in impaired immune function and increased inflammation. These effects may be aggravated in horses that experience external stressors or are training at high levels.
Signs/Symptoms of High Iron in Horses
You might suspect iron overload in your horse if you observe these signs:
- Poor coat condition – Bleaching and red ends on dark manes and tails. The coat could also have frizzy ends, generally look dull or rough and shedding in patches.
- Hoof problems – Laminitis and abscesses are common in horses with high iron. You might observe hoof wall cracks, thrush and/or white line issues even with good hoof care and thrush treatment.
- Raised liver enzymes (AST, ALT, ALP) in a blood test could suggest liver damage due to high iron levels.
- Intolerance to sugars or insulin resistance not necessarily related to obesity or high sugar intake.
- Cushing’s disease/PPID (pituitary pars intermedia dysfunction) â€“ these conditions often coincide with iron overload.
- Allergies/immune issues â€“ if your horse has frequent infections or has a hard time recovering from illness they might have high iron. Allergies to dust or pollen might also be a sign of a weak immune system due to high levels of iron.
Tips to Lower Iron Intake in Horses
- Avoid feeding hay on the ground whenever possible to lower your horse’s soil intake.
- Soaking hay in water can remove a lot of iron, but this might also affect other minerals.
- Forages that are grown in acidic or high clay soils will likely be higher in iron. Discuss this issue with your hay provider or consider applying limestone to your fields to increase the soil pH.
- Grass and forage grown in areas with high rainfall will have higher iron. Consider this factor when choosing a hay provider if possible.
- Test your water iron levels and consider adding a water filter to remove excess iron.
Determining your Horse’s Iron Status
Blood tests can be done to determine your horse’s iron status. Serum or blood levels of iron alone will not tell you how much is stored in the body. Serum ferritin is a good indicator of the body’s total iron content. A study in 1984 found a high correlation between serum ferritin and iron levels in the liver and spleen of horses.. This test is still considered the gold standard for assessing iron levels in horses.
Another approach is to measure iron and transferrin levels to calculate transferrin saturation. Transferrin is a protein in the blood that carries iron to tissues that need it. The percent transferrin saturation is calculated by dividing serum iron by transferrin and multiplying by 100.
In horses, transferrin saturation in horses is typically around 30-40%.  Horses with chronic iron overload can have transferrin saturation levels exceeding 80%.
Horses with such high levels have clinical signs of iron overload including haemochromatosis (excessive iron absorption) and hepatopathy (liver damage). 
When transferrin saturation is high, the horse’s ability to bind excess iron onto transferrin will be limited. This means that there will be more free iron atoms that can act as free radicals causing oxidative damage throughout the body.
Horses with Metabolic Conditions
High levels of iron in the body are particularly a concern for horses with equine metabolic syndrome (EMS) or insulin resistance (IR). Research in humans and animal models has revealed several ways that iron and insulin sensitivity are linked.
Elevated levels of this mineral in the body can predict future insulin resistance and are a consequence of insulin resistance. In humans, this is known as dysmetabolic hyperferritinemia.
Horses with high levels of insulin in the blood, a typical feature of insulin resistance, have also been found to have high levels of ferritin.
This means that horses with metabolic syndrome are likely to have excess iron in the liver which puts them at risk for liver damage. This also suggests that the links between iron and insulin resistance found in other animals exist in horses. 
Cushing’s disease also known as pituitary pars intermedia dysfunction (PPID), is a condition that looks similar to EMS. Both EMS and Cushing’s can involve changes to fat distribution, insulin resistance and laminitis.
Cushing’s disease/PPID usually occurs later in life than EMS and is due to dysfunction of the pituitary gland in the brain, whereas EMS is primarily an issue of insulin resistance.
Horses with Cushing’s disease/PPID are at high risk of infections due to an impaired immune system. Iron status and intake should be closely monitored in these horses to avoid making the problem worse.
Iron in Equine Supplements and Feeds
Acute iron toxicity in horses is usually linked to ingestion of feeds or supplements that contain excess amounts of this mineral. Over-supplementation is more common in performance horses and young foals.
The nutrient or composition analysis of equine supplements will usually show that there is iron in the product even if it is not specifically added as an ingredient. This is because iron is found in all plant materials and in some mineral or vitamin ingredients. It is impossible to completely eliminate iron from premixes.
Some commercial equine premixes will have iron specifically added to the product and should be avoided. To find out if the product you are feeding contains added iron, scan the ingredient list for compounds such as iron oxide, ferrous furmate, ferrous sulfate or ferrous gluconate.
Iron sources like ferrous furmate appear reddish-brown in colour. Salt licks that appear reddish-brown likely contain added iron.
Iron is added to some commercial supplements, likely because it is incorrectly thought to improve exercise performance by increasing the oxygen carrying capacity of red blood cells. Research has shown that this is not the case. 
Simply adding more of this micromineral to the diet will not increase the red blood cell count or oxygen delivery to muscles. Supplementation is more likely to cause problems related to liver damage, oxidative stress and mineral imbalances.
Mad Barn’s vitamin/mineral premixes do not contain any additional iron. The nutritional analyses will show that there is some iron contained in the products, but this is due to the natural presence of this mineral in other ingredients.
For example, our Omneity Mineral and Vitamin Premix contains 900 mg of iron per kg of product. This is the concentration in the product, which is different from daily intake. A typical serving size of 120 grams per day of Omneity Premix for a 500 kg horse would yield 108 mg of iron. Unless your horse’s hay is very high in iron, this would fall within the upper tolerable intake for a typical horse.
Mad Barn’s AminoTrace+ vitamin/mineral premix is specifically formulated as a low-iron option for horses with metabolic concerns. This product contains a low iron source of phosphorus and added copper and zinc to counterbalance the absorption of iron from dietary sources.
AminoTrace+ is formulated with monosodium phosphate instead of monocalcium phosphate as the phosphorus source. This lowers the iron concentration to 100 mg per kg of supplement. A typical serving size of 200 grams per day for a 500 kg horse would provide just 20 mg of iron.
Using a mineral and vitamin supplement like AminoTrace+ can help to minimize iron intake in horses with insulin resistance or Cushing’s disease and prevent some of the potential harmful effects of high iron in your horse’s diet.
You should always consult a qualified nutritionist before altering your feed program. Submit your horseâ€™s diet for analysis online and one of our equine nutritionists will be happy to provide a complementary review.
- Haluschak, PW and Wills, GF. Status of Selected Trace Elements in Agricultural Soils of Southern Manitoba.Research Branch Technical Bulletin. 1998.
- Walker, EM and Walker, SM. Effects of Iron Overload on the Immune System. Ann Clin Lab Sci. 2000.
- Smith, JE et al. Serum Ferritin as a Measure of Stored Iron in Horses. J Nutr. 1984.
- Harvey, JW. Iron Metabolism and Its Disorders. Clin Biochem Dom An. 2008.
- Theelen, MJP et al. Chronic iron overload causing haemochromatosis and hepatopathy in 21 horses and one donkey.Equine Vet Journal. 2018.
- Kellon, EM and Gustafson, KM. Possible dysmetabolic hyperferritinemia in hyperinsulinemic horses.Open Vet J.2020.
- Loch, WE et al. Effect of supplemental iron, live saccharomyces cerevisiae yeast and exercise on hemoglobin and packed cell volume of the blood of horses. J Equine Vet Sci. 1984.