Iron supplementation
There is a lot of discussion regarding iron supplementation in the horse industry, usually resulting in a lot of confusion! Most commercial products contain additional iron, and there are also “blood building” products containing high levels of iron that promise to treat anaemia or boost athletic performance. On the other hand, many horse owners will have heard that typical horse diets are already very high in iron, or even that too much iron may not be good for their horse. So what is the answer?
Iron is an essential mineral, mostly found in haemoglobin (red blood cells) and myoglobin (muscle cells), both of which have extremely important roles in oxygen transport throughout the body. Iron is also a part of many enzyme systems. However whilst we might be familiar with iron deficiencies in humans, it is extremely uncommon for horses to suffer from iron deficiency. Why is this? It’s estimated that an average horse requires 400mg of iron per day to meet its requirements. Forage often contains 100-250mg per kilogram*. So a horse eating 2 kg of hay may already have consumed enough iron for the day. But of course horses need to eat more than that (see this article), so iron intake can very quickly increase! And some feed stuffs, such as beet pulp, can be over 500mg/kg. To illustrate further, this is the breakdown of iron in my horses’ base diet:
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It becomes very obvious that just with forage, horses are consuming more than enough iron to meet their needs! It also seems obvious that additional supplementation of iron is simply not necessary. The next question to ask is – is all that excess iron a problem? This is less simple. The maximum amount tolerable amount is thought to be 500mg/kg of feed (so around 5000mg per day for an average horse), so levels such as those in my horse’s diet are not acutely toxic. The issues creep in when you consider how the body deals with excess iron and how iron interacts with other important minerals. Iron is not directly excreted from the body like many other minerals, rather the majority is stored in the liver, with some small losses in sweat and shedding cells of the skin and gastrointestinal tract (and of course if there is blood loss). Whilst iron absorption is decreased when stores are full, it is possible to reach a state of “iron overload”, where the body is storing too much iron. Very little is known about this in equines, however iron overload does occur in humans and can cause liver, metabolic and inflammatory problems.
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In recent years, a link has been made between excess iron and insulin resistance in horses, however it is unclear as to whether excess iron causes or exacerbates IR, or whether IR horses have a reduced ability to regulate absorption. Either way, there is no benefit to adding more iron to the diet, so best to play it safe and avoid additional iron. Additionally, high levels of iron suppress the absorption of copper and zinc – both very important trace minerals that are typically lacking in common feeds. Bleached coats and poor quality hooves are a common symptom of this. Correct ratios between these 3 minerals need to be maintained, and to balance the already high iron levels, additional copper and zinc is already required in most diets. The more iron in the diet, the more copper and zinc need to be added – so why add more iron?
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All in all, there simply is no good reason to add iron to horses’ diets, and a few good ones to avoid or reduce it. Why do so many companies add iron to their products and promote it as beneficial? I don’t know, and it is one of the reasons horse owner’s need to be careful about which supplements they choose. Integral Equine Nutrition’s custom equine supplements do not contain iron (or anything else your horse doesn’t need!).
* Some feed companies that include iron in their products will point out that dietary iron absorption from plants is low, around 10-15%. This is true, however the dietary requirements recommended by the National Research Council already take this into account, so it is not a reason to supplement more iron.
* Some feed companies that include iron in their products will point out that dietary iron absorption from plants is low, around 10-15%. This is true, however the dietary requirements recommended by the National Research Council already take this into account, so it is not a reason to supplement more iron.