We always consult our panel of veterinarians when formulating new products, but we also often get questions from veterinarians about the properties, composition and effectiveness of the products. One of the questions is:
Does the horse need iron in its supplementary feed?
Is it safe to give an EMS horse iron?
Iron is a trace mineral that is necessary for both plants and animals. There is typically between 1-5% iron in the soil and it is taken up by plants to a variable extent, but when it reaches the horse in the form of hay, most of the iron is in insoluble oxide forms that are not easily absorbed by the horse.
Iron has many functions in the body, such as:
- oxygen carrier in the hemoglobin of red blood cells
- myoglobin in muscles
- energy production co-factor, inside the mitochondria of cells
- defense substance in the white blood cells' defense against infections
Iron from the feed is absorbed in the small intestine and approximately 75% is found in the liver, spleen and muscles.
Some are found in a subgroup of white blood cells, the macrophages, and they are thus a very important component of the immune system, as the macrophages are responsible both for initiating the immediate (innate) immune defense in the event of infection, but also for stopping immune activation when an immunological event has occurred/is over.
Iron metabolism in horses
Iron is absorbed by transporter proteins across the intestinal mucosa via a hormone called hepcidin. Hepcidin controls how much iron enters the bloodstream and how much is available to immune cells. When the blood cells die, the iron is excreted via the bile into the intestine. This is to avoid too much “free iron” (Fe2+), which can cause oxidative stress damage to cells and tissues.
After absorption, iron is transported, bound to transferrin, so that hemoglobin and myoglobin can be produced, and it is stored in a suitable depot in the form of ferritin- or hemosiderin-bound iron.
Horses need approximately 40 mg of iron per kg of dry matter in the feed – i.e. a 500 kg horse consuming 10 kg of dry matter must have a minimum of 400 mg of iron. Foals and young horses in growth, including pregnant and lactating mares, need a minimum of 50 mg/kg of dry matter. The need also increases with moderate and vigorous physical activity/training.
Iron in the feed
When analyzing feed materials such as grass, hay, wrap, beet pulp, etc., a high iron content is often found. Some of that iron may be due to contamination/admixture from soil.
Iron from straw feed is not easily absorbed.
Iron from straw feed is not easily absorbed, estimated at perhaps 15-20%. Partly because of the form in which iron is found in plants, and partly because of the fibers that also bind the iron in a form inaccessible to the small intestine.
Iron can be released from the fibers in the microbiological fermentation of the large intestine, but is not absorbed in this intestinal section, so it is transported out with the manure. Horses are fully capable of regulating the absorption of iron across the intestinal mucosa and horses have adapted over thousands of years, including in parts of the world where there is much more iron in the soil and in the grass than there is in Denmark.
EMS and iron scare?
There is a study that has found iron overdose and toxicity in horses. Many studies have been done for toxicity, including both ferritin and, what's more, the accumulation of hemosiderin in organs and tissues. But the iron came from the drinking water and not from the feed. Iron in water is found in the more easily absorbable Fe2+ form, in contrast to the usual form in the straw feed, Fe3+.
It has also been shown that horses with metabolic problems, such as insulin resistance/EMS, have elevated values of the iron storage protein ferritin, but the same study shows no correlation between current iron values in the horse.
We know from human studies that ferritin can be increased for many reasons other than real iron overdose, for example inflammation, joint diseases, liver strain and cancer, etc. It is assumed that a significantly elevated ferritin level should be further investigated with, among other things, measurement of transferrin saturation (normal values exclude iron accumulation), inflammation markers, iron binding capacity, etc. In humans, there are genetic variants that cause too much iron to be absorbed, but this is rare.
No causal relationship has been demonstrated between iron in the feed and insulin resistance, nor have studies been conducted to reduce ferritin or the true iron depot in horses with Equine Metabolic Syndrome (EMS).
"Horses are quite tolerant of iron intake and it is estimated that they can tolerate approximately 10 times the normal requirement without developing insulin resistance."
Horses with EMS may have a disturbed regulation of iron absorption because the liver may be affected by blood sugar-insulin related inflammation. It is therefore very important to provide sufficient physical activity/exercise for these horses, as this is one of the factors where there is a causal relationship between insulin dysregulation and the development of EMS.
In order for horses to tolerate regular exercise without getting sore and tired muscles and thus being at risk of joint and tendon damage, it is crucial that their energy production works. Optimal energy production requires easily absorbable iron, along with other minerals and trace minerals such as magnesium, copper, zinc, manganese, selenium, iodine, molybdenum, cobalt and salt.
Most health problems in horses are multifaceted. Iron loss should be considered, for example in connection with severe immune system effects, stomach ulcers and sweating.
Horses that sweat a lot, for example during vigorous physical activity and in a hot climate, can produce up to 20-30 liters of sweat per day. They thus lose at least 400 mg of iron in sweat alone, 21 mg of iron per liter of sweat.
Why do we do what we do?
It is difficult to quantify the horse's absorption of iron from straw feed, as there is a lack of in-depth research in the area.
The iron in straw feed is mostly in insoluble oxide forms that are not easily absorbed by the horse, and there is no factual knowledge about how much of the other forms of iron in straw feed the horse is able to absorb.
We choose to add the absorbable and biologically readily available iron to the vitamin and mineral supplements Every Day Happy and Peak Performance, as iron is a very important component of the immune system and is essential for many of the horse's various biological functions.
The proportion of iron that comes from Every Day Happy and Peak Performance constitutes approx. 20-30% of the total iron intake together with straw feed. Example: 500 kg horse in light work/fold, is given 250-300 grams of EDH/PP daily, corresponding to 320-384 mg of easily absorbable iron. 10 kg of wrap in slipway (70% dry matter) provides 900 mg, while 5 kg of spring barley straw provides 666 mg of iron, but of completely unknown absorbability.
Horses have good regulatory mechanisms to manage the iron balance from their feed, and even horses with EMS need iron to be able to exercise and get back into better metabolic shape.
When feeding Regulator Completes Every Day Happy or Peak Performance you can easily calculate how much your horse is getting daily, as they are the only sources of vitamins and minerals. Our fibermash products do not have added vitamins and minerals.
If you have any questions about iron in the feed, you are very welcome to use the comments field so that others can also benefit from the answer.
Scientific sources
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If you have any questions about iron in the feed, you are very welcome to use the comments field so that others can also benefit from the answer.
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