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Iron In The Horse's Diet: Careful Monitoring Is Needed To Maintain Equine Health

Iron is an essential micromineral in the horse's diet and nature has provided an abundance of it in soils, plants and water. Yet we find that many horse owners give supplemental iron without realizing the consequences, believing that this is the "energy boost" that a horse needs. Deficiencies in this mineral are very rare while excess amounts are all too common and can affect a horse's health in detrimental ways. If your horse has any immune issues, metabolic conditions, infections, or laminitis pay extra attention to iron levels in the diet. I always advise to get your forage tested to determine the iron content and supplement from there to meet the horse's requirements.

Always have your horse's blood tested before you supplement with "blood builders", else you may be putting your horse at unnecessary risk. Here is a breakdown of quick facts you should know about iron (Fe). In the examples below you will find that a typical diet (even a just forage diet and water) can provide higher than recommended amounts of iron for the horse. [All values are expressed on a Dry Matter Basis (DM); ppm (mg/kg) refers to concentration in the total diet; NRC refers to NRC's Nutrient Requirements of Horses, 6th ed.]

Iron Importance: Iron is found in four areas in a horse's body and is an essential component of blood hemoglobin protein (60%) and muscle myoglobin protein (20%); 20% is found in the blood, bound to two proteins called ferritin (iron storage), and transferrin (for blood transport); the iron in the blood carries oxygen to all cells in the body (cellular respiration). Iron is also found in the enzyme systems.

Daily Requirements (NRC): 50 ppm fed for foals (excluding newborns), pregnant and lactating mares, and 40 ppm fed for mature horses.

Examples: Forages, feeds, grains and supplements will have varying amounts of iron (Fe) mostly because of the soil conditions the plant is grown off of (forages, grains, feed components), or as a result of natural or synthetic additives (commercial feeds and supplements). For example the minimum requirement for a 400 kg horse that is not exercised is just 320 mg iron per day (NRC).

Forages typically have 50-500 ppm Fe (250 ppm average); Cereal Grains have 20-100 ppm Fe.

Recommendations: While most healthy horses have a wide tolerance to iron levels beyond the 40 ppm recommendations (to a maximum of 500 ppm) many horses are sensitive to high levels of iron in their diet. If the horse is overweight, insulin resistant, has/had laminitis, or PPID (Equine Cushing's Disease), adjust your feeding plan to one that is closer to the NRC requirements. A horse with any of these conditions is usually extremely sensitive to high iron levels, and will require careful monitoring of the diet. Iron is commonly found in forages (have your forage tested), in all feeds (even if it neglects to show the iron content on the feed tag), supplements, grains, and other horse feedstuffs. If in doubt contact the manufacturer for the iron content and they would be happy to give you it to you. Iron is extremely easy to over supplement!

Iron Deficiencies: Rare in normal, healthy, growing and adult horses; deficiencies are measured by reduced blood ferritin levels (not iron levels); results in decreased exercise capacity; could lead to anemia. Deficiencies are most often due to blood loss; likely a secondary problem exists and vet should be consulted. Foals are born with a high tissue concentration of iron and so do not require supplemental iron/ iron injections especially in the first two weeks of life.

Iron Supplementation: No known benefits for non-anemic horses. Iron injections should not be given to horses unless tested and advised by a veterinarian; injections can cause severe reactions or death. Some ulcers may cause internal bleeding which can result in significant blood loss. Best to have a blood test done by your vet to determine if supplementation is really necessary. Iron, as in all minerals, needs to be balanced with other minerals such as Copper, Zinc and Manganese to maintain good health. A typical balanced ratio would be in the range of 4:1:2:2 to 10:1:4:4 (Iron: Copper: Zinc: Manganese). When supplementing with iron, always consider the other minerals involved.

Excess Iron: Maximum tolerable level for iron is 500 mg/kg of feed (ppm) per day (NRC). Excess iron is problematic: decreases disease resistance and immunity, decreased athletic performance, iron accumulation in organs leading to liver failure; iron is considered an antagonist - causes interference with the absorption of other minerals ie copper, zinc and manganese, leading to other health issues;. Excess iron can lead to depression, dehydration, diarrhea, insulin resistance (and laminitis), and increased risk of bacterial infections. Supplemental iron can be toxic to foals.

Iron and Immune Function: Too much or too little iron can negatively impact the immune system. Since iron deficiency is rarely seen, immune function can be suppressed by too much iron, which can sustain an existing bacterial infection. For example, in the case of hoof abscesses, high iron intake may affect abscess healing. Horses with PPID (Cushing's Disease) are at a higher risk of a depressed immune system so it is extremely important to monitor iron levels in the diet. Always have your forages analyzed in these cases and choose forages, feeds, vitamin/mineral supplements low in iron meeting or slightly exceeding the recommended daily amounts.

Iron and Insulin: Studies have proven that too much iron in humans can increase insulin resistance, which can only be stopped by removing supplemental iron from the diet. There can be a correlation in horses that excess iron can interfere with insulin levels which in turn can lead to laminitis. If a horse has chronic laminitis it is well worth examining the diet for excess amounts of iron.

Iron Status: Before supplementing with any iron product it is best to have your horse's diet evaluated and your horse's blood tested. This can be done by a TIBC test (total iron binding capacity) plus a TSI test (tranferrin saturation index). Provide your horse hay before drawing blood for these two tests as fasting can cause false low readings. Another test that is used is testing ferritin levels. If this protein is low, anemia may be suspect. Infections and cancer can cause high ferritin readings because these cells rely on iron to multiply; the body tries to protect itself by removing circulating iron from the bloodstream and puts it into storage.

A Typical Feed Program:

* ppm = mg/kg (fed)

If you have a 500 kg working horse (1270 lbs) and feed 2% BW hay, this amounts to 10 kg of hay. Hay typically contains 50-500 ppm iron, so we will use 250 ppm as an average. Add a hay balancer feed fed at 0.25 kg/100kg BW (contains 400 ppm iron) and 0.5 kg of oats to the diet (typically containing 106 ppm iron). This horse requires a minimum of 500 mg of iron per day (NRC).

Therefore, going through the calculations, the hay gives 2500 mg Fe, the feed is 500 mg and the oats is 53 mg for a total of 3,053 mg of Iron in the diet. Total weight of the diet is 11.75 kg so the iron concentration is 3053/11.75 = 260 ppm. So we can see from the typical diet that a horse receives more than enough iron in the diet but within the maximum tolerable amount of 500 ppm. While healthy horses have a wide tolerance for iron in their diets, many horses that are prone to health issues do not, and should meet or slightly exceed the NRC recommendations. This may mean finding hay/pasture and supplemental feedstuffs low in iron.

Another Example:

My 10 year old horse has PPID and is now on a low iron diet: I managed to find hay with 91 ppm iron, combined with a small amount of commercial feed and a low iron vitamin/mineral supplement to balance her diet. The total amount of iron in her diet (excluding water) is approximately 900 mg, giving her an iron concentration in the diet a value of 92 ppm (far below 500 ppm). Previous to the diagnosis she was on hay showing 242 ppm (DM) iron, which would have meant that she was receiving 2300 mg of iron (DM) just from her hay! Historically, she was prone to various infections. Her treatment plan includes pergolide and a low iron, carefully selected and balanced diet - a much healthier and happier horse as a result!

In both examples I did not include the iron concentration in the drinking water - something that is worthy to note if the water is high in iron. As you can see it is very easy to meet the iron requirements of the horse, not to mention nearing the maximum tolerance level.

To maintain good health for your horse, always analyze the hay and balance the nutrients in your horse's diet. Feed My Horse Equine Nutrition Software makes it easy to monitor iron levels in your horse's diet to keep your horse healthy!




1. NRC's Nutrient Requirements of Horses, 6th edition

2. The Horse Nutrition Handbook, Melyni Worth

3. Nutrition and Feeding Management For Horse Owners, Novak & Shoveller

4. Feed Your Horse Like A Horse, Juliet M. Getty


Healthy Horses. Happy Owners. Superior Results!

Superior Equine Health and Nutrition Inc. ~

The articles contained in this column are for the purpose of education and are not intended to take the place of proper veterinary care. They may be used in conjunction with such care to facilitate healing and maintain health of the horse.

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