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.