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Australian regulations require that horses should not be fed more than 0.5 mg of selenium per kg of feed .
IRON The central role of iron is to transport oxygen around the body . Iron is abundant on earth and soil , grass , hays and sugar beet are all high in iron . There has never been an iron deficiency anaemia reported in horses except those that have a massive or on-going haemorrhage and blood loss . Iron provision to foals and iron injections have caused toxicity . There is little rationale for adding iron to diets and excess iron supply can overwhelm regulatory mechanisms . Normal diet sources should be enough . Iron never leaves the body , it is recycled . Excessive oral and injectable iron supplementation , can reduce absorption , damage red cells and cause low RBC counts in high performance horses .
MINERALS MUST BE SUPPLIED BY THE DIET . The amount of minerals a horse needs is linked to the amount in the body – but deficiencies and excesses are common . For some minerals the body can regulate how much it takes from the diet and control the amount it holds onto and how much it discards through urine and manure . What goes in must go out – right ? Not always and for other minerals there is no mechanism to control either the amount taken in or the amount discarded .
In addition , minerals interact with each other and excesses of some induce deficiencies of others .
Overconsumption of minerals induces an abnormal load in certain tissues . This is especially so for iodine and selenium . Kelp and other seaweeds are sometimes used as an iodine supplement but they often contain very high concentrations of iodine and have been implicated in cases of toxicity . Both a deficiency and an excess of iodine impair thyroid function . Selenium toxicity can arise from excessive Selenium administration due to an error in manufacturing , high levels in the water but the most common cause is use of multiple supplements . Early lesions begin as lameness and soreness of the coronary band and feet – often missed as they settle down relatively quickly .
They are followed in one or more days by the development of a crack that occurs parallel to and just below the coronet ( due to defective tubular horn produced by the dermal papillae of the coronary band ). Moderately high intakes of selenium , which are not toxic enough to cause the signs described above , may affect the frog horn and be a factor in some cases of persistent thrush .
Diagnosis of a mineral imbalance is rarely straight forward and may require blood or urine tests and tissue biopsies . Some imbalances cause acute clinical signs and symptoms . Others are less obvious . An adequate and balanced supply of minerals is important . Mineral intake from plants does not guarantee adequate intake - additional supplementation is often required . Overt excesses and deficiencies may result in obvious clinical signs , the more subtle effects of excess or marginal intakes can be difficult to detect . Although some information on requirements is available , our knowledge is incomplete - but what we do know can be applied in the feed bin .
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MARCH / APRIL ISSUE 2021