Monday, 4 November 2013

Iron: Do you know the facts?

Of all of the minerals, iron seems to be the one at the forefront of many owners mind; perhaps because we have become accustomed to associating a feeling of tiredness and not eating enough green vegetables with iron deficiency and anaemia. However, when it comes to our horses, should iron be a primary concern and is an additional supplement necessary?

Iron is a ‘micro mineral’ or ‘trace element,’ meaning that it is required in smaller amounts by the horse. Its primary function lies in oxygen transport and consequently, approximately 60% of the iron in the horse’s body is in haemoglobin – the protein which carries oxygen and gives blood its red colour.

Despite the fact that iron does not provide any energy, iron rich supplements are often propositioned as aid to improving energy levels, enhancing performance and as a ‘tonic’ or ‘pick–me-up’ for horses in hard work or recovering from illness. In truth, there is no scientific rationale to support this and iron is a great example of the fact that more does not always equal better.  Mature horses need approximately 400-600mg of iron per day, equal to only 0.4-0.6g. Iron deficiency in horses is rare even in hard working horses and tends only to occur as the result of significant blood loss (including internal blood loss). In fact, toxcosis is far more common than deficiency in horses.

The National Research Council (NRC-accepted institute for standardising animal diets) sets the maximum tolerable level for iron at 500mg/ kg of feed, although some nutritionists feel that due to the potentially high levels is some forages, this can be increased to 800mg/ kg (equal to 8-9.6g per day in a 500kg horse). Toxicosis may cause depression, dehydration, diarrhoea, an increased risk of bacterial infections, liver failure and in extreme cases death; particularly as result of over supplementation in foals where absorption is more efficient.

For the most part, iron supplements are unnecessary and should only be considered following a confirmed clinical deficiency. Although the addition of an iron based supplement will not automatically result in toxicosis, they have the potential to do more harm than good; particularly as many owners do not have their forage analysed. If poor performance is a concern and the potential for underlying medical conditions can be ruled out, consider factors such as fitness, condition, hydration, temperament and feeding a balanced diet rather than reaching for an iron supplement.


  1. Any thoughts on iron blocking the update of copper and zinc? And the impact of high iron? My grass is 605mg / 1 kg of iron on one analysis and 707 mg / kg on the other analysis. What are your views on iron blocking copper and zinc uptake, and needing to supplement more as a result.

  2. Thank you for comments. The level of iron in your grazing is certainly high although unfortunately, it is very difficult to determine the exact implications of this on your horse’s diet (if any); particularly without knowing what else he/she is currently fed - the only way to assess the nutritional status of the horse is to evaluate the dietary supply. Iron, copper and zinc are linked, competing for the same absorption sites within the body and for this reason, excess iron intake may inhibit zinc/ copper absorption. However, the links between these minerals are still not fully understood and we would not recommend adding further supplements at this stage, particularly without reviewing the rest of your horse’s diet.

    Excess iron cannot be excreted and consequently is stored in body tissues, particularly the liver. Excess iron intake may lead to an increased risk of bacterial infections (because invading bacteria rely on available iron to multiply) and toxicosis. In addition to increased bacterial infections, toxicosis can result in depression, diarrhoea and liver damage. To date, reported cases of iron toxicosis have all been in response to iron supplementation rather than forage. Whilst high levels of iron in forage should not be ignored and may still have a significant effect for some horses, it may be that the levels in your grazing are not something that you need to be too concerned about at this stage, particularly if your horse has been grazing this pasture for some time and is not showing any signs of possible toxicosis i.e. liver damage, increased infections. If you would like to contact the SPILLERS® Care-Line directly, we would be more than happy to review your horse’s diet in more detail, including any additional forage, feeds or supplements that you're currently feeding. It may also be worth having your hay/haylage analysed and we would certainly be happy to advise you on this too.